Tabitha Clark was first introduced in Twisted. When the girls were vacationing in Jamaica for spring break, they saw Tabitha, a girl who resembled Alison/Courtney very strongly. Believing that Tabitha was Real Ali, on account of her burn scars and seeming to know all of the girls' secrets, Aria pushed her off of the roof of the resort they were staying at when Tabitha seemed to lunge at Hanna. She survived the fall but was then killed by Nick Maxwell.
One day, while hanging out at the tropical rooftop restaurant of their hotel, where plenty of underage drinking is going on, Emily spots Tabitha and freaks out, as the girl looks just like Real Ali/Their Ali. Tabitha has honey blonde hair and cerulean blue eyes, just like Ali, and, even with her burn scars, she radiates beauty and confidence. However, Hanna, Aria, and Spencer think Emily is just overreacting.
When Spencer goes to the restroom, she meets a girl there, and the girl mentions that she was supposed to stay at the Royal Plantain. However, Spencer looks the place up and discovers that no such resort exists in Jamaica.
Tabitha spends time with each girl individually, giving each the sensation that she knows their darkest secrets and that she is very similar to Ali:
- Tabitha tells Spencer that she feels like they may resemble each other, like long lost sisters. Alison and Spencer were half siblings.
- Tabitha alludes to a "guy problem," then tells Spencer, "You know something about that, right?" All Spencer and Their Ali ever did was fight about guys, not to mention that Their Ali knew Spencer was cheating with her sister, Melissa's, boyfriends.
- Emily notes that Tabitha has that "I'm-Ali-and-I'm-fabulous" smile.
- Tabitha asks Emily to dance, and as Emily reminisces, "everything had suddenly felt right, just like the moment when Real Ali kissed her." This is a nod toward Emily's crush on Their Ali, who had always mercilessly teased Emily, but never sincerely reciprocated.
- Emily notices that Tabitha is wearing an old string bracelet, tattered and the same shade of lake blue as the friendship bracelet Their Ali used to wear. Hanna concurs with Emily's observation.
- Tabitha seems to be alluding to Emily's secret of not shutting the door to the Poconos house Real Ali tried to burn down with the girls in it, so that Real Ali could have escaped; when questioned by the girls whether or not she is Ali, Tabitha mentions the fact that everyone accepts that Ali didn't survive the fire: "But I escaped? Any ideas how that could have happened, Em?" She then pointedly glances at Emily's pocket "as though she had X-ray vision and could see the orange tassel Emily had carried everywhere," the same tassel that had been on the door Emily had opened when the fire was raging.
- Tabitha alludes to Hanna's chubby days, when Their Ali used to mercilessly tease Hanna for being overweight; "You're gorgeous you know . . . But I bet you weren't always gorgeous, were you?" Hanna replies, "What's that supposed to mean?" Tabitha counters, "I think you know, don't you?"
- Hanna then notices that Tabitha's "cupid-bow lips looked just like Ali's. It was as though Ali's ghost shone through Tabitha's marred skin."
- Tabitha seems to be hinting about the secret Aria kept about her father's infidelity, a secret only Alison was privy to as far as she knew. The girl mentions Noel saying, "Don't worry, he's a good boy. Not like the rest of us cheaters." (In addition, Aria had cheated on Sean Ackard with Ezra Fitz. Aria was sure neither of these stories had made it to the press).
- In addition, Aria had always felt threatened by Alison around Noel, knowing that Alison was flirting, and Noel was into it. That same jealous instinct kicks in when Aria sees Tabitha talking to Noel at the bar. Even Noel murmurs something about Tabitha seeming familiar after she walks away.
Later that night, Tabitha summons the girls to the rooftop deck/crow's nest at the resort later that night, slipping a note under their door. At this time, Aria is the least convinced of all the Liars that Tabitha is really Alison. The girls confront Tabitha, who has clearly heard about Alison DiLaurentis on the news, and they accuse her of being her. Tabitha denies it, but in doing so incriminates herself more in the eyes of the girls.
- Tabitha tells all the girls, "I feel like I've known you girls forever!"
- She uses Ali's signature line in declaring her "true" identity: "I'm Tabitha, and I'm fabulous!" The girls gasp, and now even Aria, who had been the most skeptical about the Tabitha-Ali connection is convinced that the two identities are one and the same.
Tabitha claims that she wants to show the girls the view, but she corners Hanna dangerously close to the edge. Aria screams at her, warning her to back away, but Tabitha acts offended and confused about what she considers an overreaction. She then corners Aria, and the girls are terrified that she is trying to kill them. In a moment of instinctual self-preservation, Aria pushes the girl over the ledge.
They hear her body fall to the sand below the deck. They then search everywhere for the body, wondering where it is. They assume that she either walked, which seems unlikely in her condition, or was washed away to sea; they have no idea if she survived. They expect her body to be washed to shore soon if that is the case, but it is not until almost a year later, exactly the anniversary day of Ali's attempt to kill them in a fire, when her body is discovered by a fisherman off the coast of Jamaica, and the girl's body is indeed identified as that of Tabitha Clark, a young woman from New Jersey, exactly what Tabitha had claimed. They also learn from the news story that Tabitha had survived a structural fire some years back. The girls begin to panic even more than they had been in the year the body was missing because they realized that they had killed an innocent person.
The girls' fears of being cast as murderers intensify with the discovery of Tabitha's body; however, their fears are slightly alleviated when the news anchor reports that it is believed that Tabitha's death was an accident. The Jamaican resort was notorious for underage drinking, just like they saw the day she died. Therefore, it seems logical that she was drunk and swam out to sea, drowning under the influence. However, "A" lets them know that he/she knows their secret.
In Stunning, it is revealed that the late Gayle Riggs was her stepmother, before Gayle is murdered by "A" in her driveway while the girls are looking in Gayle's house for Emily's baby. At the end of the book, at Gayle's funeral, Tabitha's father reveals that investigators have discovered that Tabitha didn't die of alcohol poisoning; she was murdered. With this information, the Liars fear that their secret will be exposed.
In Burned, we learn that Tabitha dated Graham. Noel finds her locket on the beach and gives it to Aria. Graham flips and then when Aria opens the locket she sees Tabitha and Ali inside. When the liars are about to confess to Tabitha's murder, the news comes on and it is revealed that Tabitha actually died from blunt-force trauma to her head, having survived the fall. Just after this news announcement, the Liars get a text from "A," in which "A" admits that she/he killed Tabitha, and that they are next.