|“||I'm coming with you. I don't really care that you're pissed at us, okay? I care that you're safe.||”|
— Spencer to Alison
Alison's relationship with Spencer is very different. Spencer and Alison were always fighting, trying to out-do each other constantly. Alison usually leaves Spencer annoyed with her and Alison distressed because Spencer is the only one of the four girls who could ever stand up to Alison, which first comes apparent in "Pilot", when they have their argument in Spencer's house, the night of Alison's disappearance. There, Ali threatens to tell Melissa about Spencer's kissing Ian Thomas or else she will. Spencer yells at her that if she says one word to Melissa, she'll tell everyone the truth about The Jenna Thing. Also in "If At First You Don't Succeed, Lie, Lie Again", she is again seen pressuring Spencer to tell her sister about Ian. Spencer is the most like Alison, as they are both smart, determined, sophisticated, and will do just about anything to be the best. In "The DArkest Knight", it is revealed that Spencer is Alison's maternal cousin via Mary Drake, who is Alison's Aunt and Spencer's biological mother. The pair are also both sisters to Charlotte DiLaurentis - Spencer by blood and Alison via adoption.
Spencer flashes back to a moment the summer before, when Melissa Hastings was dating Ian Thomas. She had been standing with Alison and Hanna in her kitchen when Ian and Melissa walked in. Suddenly, Alison announced that Spencer had something to reveal, but Spencer denied it, and was annoyed by Alison's blunt betrayal. She replies with "outside" and gestures to the back door. Alison had threatened to expose Spencer's secret in front of her sister, namely the fact that she had once kissed her sister's boyfriend Ian. She tells Alison that if she says one word to Melissa, Spencer will reveal the truth about The Jenna Thing .
After the flashback, Spencer looks out the window and sees into the window of Alison's house across from hers, a wavy blonde figure moving about inside. Spencer gasps, "Alison."
Spencer recalls in a flashback who else was at the beach that day. Jenna Marshall had come to start a barbecue, wearing her now familiar shades before taking them off. Alison expresses her annoyance, and Emily comments on Toby's conspicuous absence. When Alison responds by joking about him being busy making animal sacrifices, Spencer rolls her eyes and points out how typical it was of Alison to taunt others. But, she softens when the girls all agree that this day was perfect, and then shares their dream that they would stay friends until they grow old.
Spencer tries to convince Melissa to reunite with Ian. Afterwards, she flashes back to the previous summer when she had been practicing her field hockey swing on the front lawn. Ian had walked by, and, under the pretense of correcting her technique, put his arms around her waist and leaned in to kiss her neck. Surprised, Spencer had turned around to face him, and this, too, ended in a series of mouth kisses. After Ian walked away, Alison called out from where she was standing a few meters away to let Spencer know that she saw her kissing her sister's boyfriend. She called it disgusting and basically called Spencer a skank to boot, implying Alison's jealousy.
Spencer guiltily recalls how the night she disappeared, Alison had pressured Spencer to tell her sister about kissing Ian, something that would've left Ian all for Alison. Spencer refused, but Alison warned that Melissa would find out the next day, whether Spencer told her or not. Alison arrogantly claimed that Spencer and the other Liars were her puppets. Spencer furiously countered that she was sick of her games, that she would tell Melissa, but Alison was dead to her already. Alison appeared distraught, then left angrily, and after a moment's pause, Spencer marched outside after her.
Spencer has a flashback of a time Emily was sleeping over at her house. Alison knocks on the backdoor, and appears to be enraged. Her brother is having a noisy party, and implies his friends, or "animals", as she call them, are harassing her. Spencer tells Alison she is welcomed to stay, to which Alison replies "Thanks". She grabs an apple and goes to wash it. She looks at her reflection in the window, and looks like she is about to cry. Spencer asks if shes okay, and Alison returns to her normal self. She says she was just thinking about her grandma. She eats the apple and wrinkles her nose in disgust. "Your family has the worst apples", she says.
While the girls are walking home from school in October of 2008, Spencer is seen texting on her cell phone, getting updates about her success in the school elections for class president. She just found out that she's secured the debate team's votes. She tells the girls the news using words from her large vocabulary, leaving them a bit confused. Alison sarcastically asks her if she was going to recite the entire dictionary.
Spencer is in her living room making something on her sewing machine when Alison comes knocking. Alison informs Spencer that a friend on the election committee has let her know that Spencer may not win the election. Alison tries not to be too harsh, telling her that it will be close. Spencer is crestfallen, afraid of her parents' reactions. Alison uses the opportunity to bash Melissa for purposely trying to outshine Spencer in her parents' eyes. After all, Melissa had made some of the phone calls in inviting people to Spencer's congratulatory party. Her motive in creating the sibling rivalry is not totally clear. She toys with the needles and stabs one deep into the holder near the sewing machine as she talks. Ali offers to fix the election for her, and Spencer accepts.
Later in the school hallways, Alison suggestively lets Spencer know that it has been taken care of. When the other Liars question her comment, she lies that she had helped Spencer with her speech. Next, there is an announcement over the school loudspeaker that the election results are in, and Spencer Hastings is the winner. Smiling, but insecure, Spencer accepts people's congratulations, and Alison winks knowingly at her.
On Halloween during Noel Kahn's party, Spencer joins a sulky Alison out on the porch. Alison calls Jenna a slut and hands Spencer the ballots of incriminating evidence. Spencer burns them in a nearby fireplace without looking inside, though Alison cryptically tells her that she would be surprised to know who your friends aren’t and suggestively glances Aria's and Hanna's way.
When Spencer tries to understand what is it that links Jason to her family, she flashes back to a night when Alison and Spencer were in Spencer's bedroom. Alison was reading a magazine and Spencer studying for a test. They heard Spencer's parents arguing downstairs and Alison asked what it was all about. Spencer told her that her father saw Melissa and Jason making out the other night and he's upset because of that. Alison wanted to open the door to hear what going on exactly and then said that Melissa and Jason would be "a match frowned upon by the gods." Spencer didn't catch her drift until over a year later.
Spencer wakes up in the middle of the night in her living room to find Alison rummaging through the bag Jason gave her. Alison asks Spencer not to scream, claiming she only needs something from the bag. Alison asks Spencer if she is mad at her for never telling her about Jason being her brother too. Alison says that by sharing a brother, it practically makes them sisters and that Spencer deserves a more decent sister. If she had told Spencer the truth about Jason, it would have changed everything, and Alison didn't want that. Alison sees a bottle of pain killers on the living room table, and asks to take a couple "for the road."
Spencer informs Alison that Aria met with Duncan Albert and he told her that he flew Alison back from Hilton Head the day she disappeared. Alison says Duncan "talks too much," but states she is glad that the girls haven't given up. She also says that it is now helpful the girls have the bag. She gives her a hint by telling her to look at the big picture instead of scrutinizing the individual pieces. Spencer asks what is in the bag that is so important, but Ali says she can't say. She states she misses Spencer and that everything the girls are dealing with is "some seriously messed up stuff." Ali informs Spencer, "here's the good news, you're getting warmer." Suddenly, Spencer and Alison hear a noise coming from upstairs, so Spencer stuffs the bag underneath the couch and falls back asleep. In Season 4, its revealed Ali is alive, meaning Ali really did go into Spencer's house.
Spencer finds Alison's beloved anklet in antique shop, reminding her of a night Alison had come over for a sleepover. Spencer notices Ali's charm anklet and Ali says it was from a friend, not a boyfriend, and that Spencer doesn't know "her." Ali had come over to watch movies with Spencer, but then ditches her to go to a party in order to get the girls fake IDs so they can get into frat parties and have a great summer. Spencer is upset, but as usual Ali gets her way. Her friend is waiting to pick her up downstairs.
Spencer figures out that she is staying in the same room Mona Vanderwaal stayed in while she was in Radley. On the dresser, someone engraved "Will The Circle Be Unbroken?" signed by A, and Spencer has a flashback of when Alison and her were in church. Everyone was singing the Christian hymn "Will The Circle Be Unbroken?" and nerdy Mona was there too, and she was singing the song loudly while moving her head. Alison saw her and began laughing. After church, Spencer and Alison leave while Alison makes mean remarks of Mona to Spencer. Spencer sees Mona standing alone at the top of stairs to the church, and feels a bit of remorse. Alison takes out her diary and Spencer asks if she could see it. Alison says yes, but mockingly pulls it away, and says Spencer could read it when she's dead. Spencer says "Ew, don't be so gruesome!" to which Ali replies she's just being mysterious. Spencer says she doesn't want to read her "stupid" diary, but Ali says she does, and that she's writing them for her. Spencer asks "Them?" and Alison says, "They're beyond scandalous. Your gonna need them if your gonna carry on after I'm gone." Spencer asks, "Carry on with what?" Alison smiles but doesn't say anything, and she drags Spencer to get some muffins.
Spencer has an encounter with Alison while she is staying in Radley Sanitarium . Upon following a map left by Mona, Spencer comes across a very calm Alison listening to the song "I'm Your Puppet" on a record player. The both of them briefly dance together as Alison remembers her first boy-girl dance in the sixth grade. However, Spencer clarifies and states that she never knew her in the sixth grade. Alison then replies by saying that the girls didn't know her when they knew her. After asking how she got a scar on her lip, Alison responds by saying that "girls fight dirtier than boys," implying that it was a female who attacked her a few weeks before being buried alive. Alison eventually leads Spencer to a toy rocking horse where she finds Mona's fake staff I.D. (labeled Ali Dee) and CeCe's authorized pass for visitation. Much like the previous visits, it is left unclear to the audience whether Alison was physically there or not, as Spencer hadn't slept in three days. When Spencer turns around, Wren Kingston is standing in Alison's place.
Red Coat lands in the woods in a plane. Spencer attempts to follow her, but loses her trail. However, before she does, she catches a glimpse of her face and thinks it is Alison. When Emily, Hanna, Aria and Mona come to after being dragged out of the fire, Spencer comes back and says "Ali is Red Coat."
Some of the girls believe Alison is still alive out there while some aren't so sure. The liars are in Ravenswood when Emily is suddenly captured and they go rescue her. There they discover Red Coat but then see another Red Coat. who in fact saves Emily. Spencer runs after that one while the girls corner the other one. Spencer then goes back and shows the girls something. A's lair. Spencer believes Alison was the Red Coat that led her there as she waited for her. Later in "Grave New World," it is revealed that Alison is alive, and was in fact one of Red Coats.
Spencer and her abuse counselor Dean go out for a jog. During the run she spots a shovel and starts flashing to chasing Alison. She brings the shovel down on Alison and blood hits her in the face. Spencer tells Dean "I think I know what I did." Inside she tells him she's using other people memories to fill her the blanks of her memory. She cries but stops short of telling him what she thinks she did to Alison.
Spencer steals papers from Ezra's apartment. She reads one that says CeCe witnessed a fight between Spencer and Alison the night Alison went missing. Spencer has a flashback, which is continuing the flashback from "If At First You Don't Succeed, Lie, Lie Again." After their argument inside Spencer's house, Alison storms out. Spencer follows, angrily yelling at Ali to stop. Alison says that they are over. Spencer grabs a shovel and Alison yells "You are way out of your league, Spencer"! Spencer lifts the shovel, and says "Am I? You sure about that?". Alison looks a bit scared and says "Why don't you put that thing down before you hurt yourself". Spencer doesn't remember what happened next, but the paper says Mrs. DiLaurentis also witnessed the fight and paid CeCe not to tell. Spencer fears she could have been the one who tried to kill Alison.
Veronica Hastings has a flashback of a time when Spencer was using drugs for the first time.
Spencer and Melissa had gotten into a huge argument and trashed each others things. Alison walks up to Veronica who is outside cleaning up the huge mess. She is visibly upset. Alison asks to help, but Veronica tells her to leave. Veronica says she doesn't understand whats happening to her family. Alison says she wishes she knew too. Alison turns to leave, when she sees a sick-looking Spencer staring at her.
Alison reunites with the four girls and greets them all with hugs, except for Spencer. Spencer breaks down in tears later as she wonders aloud whether she actually hurt Alison or not, but Alison alleviates her fears by revealing that the night she went missing, Alison went back to the barn to find a crazed Spencer, waiting for her. After the fight in the kitchen, Alison walked out and when Spencer followed with the shovel, Spencer tripped and the amphetamine pills fall out of her pocket. Alison pieced two and two together, and swore not to tell. She walked Spencer back to the barn and watched Spencer fall asleep. To Spencer's relief, shortly after, Alison walked home and was knocked unconscious with a rock, concluding that it wasn't Spencer who hurt her that night. Alison also reveals that she was the hooded person who saved Spencer from Ian in "For Whom the Bell Tolls."
Alison returns to Rosewood with the girls from New York. They plan on going to the police station and finally tell the police everything concerning Alison's disappearance. However, when Alison goes to talk to Officer Holbrook, she fabricates a story that the girls didn't discuss. Later, Spencer furiously tells Emily that they are back on “Planet Alison.” She screams and says that it feels like 9th grade all over again and they are in a whirly girlie ride, and is surprised that Alison expects them to back up her story.
The next day, Spencer and Emily goes to visit Alison at her house. When Spencer and Emily tell her their theory of Jason tracking them in New York and possibly being her attempted killer, Alison becomes defensive towards Spencer, and skeptically asks her if she should be afraid of their big brother. Alison tells Spencer that she knows that she told Jason about his true parentage, and asks her if she thinks that's why Jason threw a rock at her, and why her mother covered for him. Spencer replies that there was so much animosity between their families, that Jason and her mother may have wanted to shut her up to keep the truth a secret. Alison also reveals that she made up the story to the police to protect Aria. Spencer yells at Alison that she should have consulted them first before lying, and to tell them everything beforehand, so that they are not left "paddling like idiots."
While Spencer researches on rodenticides and it’s effect on humans, she receives a text from Alison which read ‘Need to speak to you. Call me.’ Alison is seen in her living room going through a page on the internet where the people she bullied posted a lot of mean things about her after she went missing. Spencer arrives and takes the laptop from her, asking her to not look at those things. Alison thinks she should leave. Alison tells Spencer that Jessica had Losartan in her system which was for high blood pressure. Since Jessica had low blood pressure, Losartan made her heart stop working. Spencer is shocked and thinks her father killed Jessica. Alison says she knows the feeling. She is still struggling to find a reason good enough to make Jessica let Alison’s attempted murderer just walk away. They talk about monsters and how they were once upon a time under their beds and now there just out there.
Spencer, Alison, Emily and Hanna are in Hanna's bedroom discussing the break-in at Hanna's house. Alison staged the break-in with Noel Kahn, since L.t. Tanner has been on her back about their kidnapping story. Spencer reminds Alison that it was her story. Spencer wonders what Alison would have done if she and Noel got caught playing the trick on Ashley Marin and if one of her excuses would have been that she needed to borrow butcher knife. Alison thinks Spencer is ‘a little loud’ and Spencer says that Alison is a ‘little crazy.’ Suddenly Alison’s phone starts ringing. She goes to pick it up and the just turns it off. Spencer asks her who it was; was it Noel or someone else she sneaks out to meet in the middle of the night. Alison is angry that Spencer has been spying on her and starts defending Noel as someone who she can at least count on since her best friends don't seem to have her back, Aria, didn't respond to her S.O.S. message and Spencer is shadowing her as if she is the enemy. She admits that stunt she pulled with Noel’s help was not the best idea but apparently she is running out of choices. Alison starts walking outside tells the girls that she is going to call her dad and she wonders if Spencer will follow her or set up a camera. At school, Alison approaches Spencer at her locker. Alison tells her that Tanner is at school to question the girls. Alison tells Spencer that her dad will be rushing back to Rosewood after he heard about what happened in the Marin house. She tells Spencer that she does not feel safe in her own bedroom. Spencer says that she needs to get to class as she has to get to the eye doctor later as well. Alison reminds Spencer that if one of them falls, they all will fall and ‘A’ will win.
Alison talks to Spencer and tells her that her father said there is no Charles. Spencer simply states that her dad is lying. Alison asks Spencer if she wants to go to the police with her Charles theory but Spencer tells her that she doesn't want to walk into the police station with any more theories and that the cops should figure it out. Ali says "Figure what out? That I am somehow related to someone named Charles DiLaurentis who really is Andrew Campbell? What do you think happened? Goblins snuck into the Campbell house and switched babies on them?" Spencer cruelly retorts "We both know that there are more conventional ways somebody can end up with more than two parents: that's how you and I got to share a brother", causing Ali to turn away from her and stay silent. Spencer then thanks Alison for getting them out of the dollhouse and hands her some juice, causing Alison to say that Spencer would have done the same for her.
Spencer stops by Alison’s house. Although Alison argues that her father has no idea who Charles DiLaurentis is, Spencer tells Alison that she needs to talk to her dad again since Spencer doesn’t believe him, and she knows that Alison doesn’t believe him either. Alison asks Spencer to leave, but before she goes she tells Alison that she is going to talk to Jason about this. Alison doesn’t want Spencer to drag Jason into this because she cannot have another person hating her, which puzzles Spencer. Alison believes that she is the cause of the all the troubles they’ve faced and blames herself for the girls’ abduction. Spencer tries to assure her that is not the case, but Alison is not convinced.
At Prom, Alison is looking for Charles and Spencer tells her to leave while she can. Alison says that Spencer never understood her or liked her and that Charles is her brother, not Spencer's; she's not going to leave until she finds out why her brother hates her so much. Later, while Spencer and Toby are discussing Alison; Spencer says that they came to the prom to protect her, something they've been trying to do for years.
Spencer: What is that?
Alison: It's my diary.
Spencer: Let me see.
Alison: No, you're gonna have to wait 'till after.
Spencer: 'Till after what?
Alison: After I'm dead!
Spencer: Don't be so gruesome!
[Spencer and Alison in a flashback]
Alison [to Spencer]: This isn't Yahtzee sweetie, this is some seriously messed up stuff.
Alison [to Spencer]: Oh, honey, you didn't even know me when you knew me.
Spencer: You think since you brought us together you can treat us like puppets?
Alison: But you are, don't you see that? You don't exist without me.
Alison [to Spencer]: Jason's your brother too, and that pratically makes us sisters right? You deserve a decent sister.
Spencer [to Alison]: What is a leader without any followers? Because it seems to me the question isn't will we exist without you, but whether you will exist without us. And as far as I am concerned, you are dead to me already!
Spencer [to Alison]: Don't you ever get tired of shooting at the low hanging fruit?
Alison [to Spencer in hallucination]: I miss you Spence. I miss that fierce look you get in your eyes when you had to know the answer - you had to win the game.
Spencer [to Emily about Alison]: We where all ready to get back to our lives and now all of a sudden we're back on "Planet Alison." It's like 9th grade all over again and we're here on the whirly girlie ride.
Spencer: It's just that, there have been monsters under my bed for so long that now there not there anymore, I feel like I have to create them
Alison: There's still monsters out there, Spence. They just might not be under our bed.
- In the books, they were half sisters, which Alison alluded to in Season 2.
- Although they aren't half sisters like in the books, they do share Jason as a half brother.
- Alison saved Spencer's life after Ian almost killed her.
- At some point in Season 4, Spencer remembers her fight with Ali the night she disappeared. Spencer, due to speeding, forgets how their fight ended, which led to her own belief of hitting Alison with a shovel, leading to her 'death'.
- In Last Dance, When Spencer tries to prevent her from meeting with Charles. Alison tells Spencer that Spencer's never understood her and never even liked her. However, this was proven to be a false statement later on.
- They are maternal cousins.