There's some random girl named Veronica who keeps popping up in this book. She apparently tried to steal Todd from Liz at one point but I never read that book. Elizabeth really, really doesn't like her but Jessica tries to get her to relax and says that she's reformed or something.
While at lunch, Ellen brags about her earrings, which her mom let her borrow. They're from Mexico and super heavy, so she takes them off and leaves them on the table when they all run off to get fresh brownies. When they come back, her earrings are gone. Despite everyone looking for them, no one finds them, and Ellen's mom is so mad that she grounds her for a week.
This leads to a rash of thefts but only of girls who are Unicorns. Someone steals Mandy's new hat, Janet's hairbrush, Mary's denim jacket, and Ellen gets hit again when someone steals her deodorant. The worst is when Lila starts watching her new Watchman, a tiny television that her dad bought for her. She and Jessica start fighting over it, and their teacher takes it from them. When Lila goes to get it after class, she finds that someone stole it from the teacher's desk.
They finally decide to go to the principal, and he agrees to tell other teachers what happened so everyone can keep a look at for the missing items. Later that same day, Lila comes storming down the hall and seems especially pissed at Jessica. She demands that Jess open her locker, and everyone finds the Watchman inside her locker. The principal brings her in for a discussion but after checking her locker, finds none of the other missing things. He lets her know that they need to talk about what happened and that she faces suspension.
Everyone believes she was the thief, who they dub the Sweet Valley Swiper, and the Unicorns stop talking to her. Liz doesn't really believe that she's innocent either. Apparently, Jessica borrowed a sweatshirt and a skirt and never gave them back. Liz finally decides that she does believe her and enlists Amy to help her find the real thief. They bring back the Snooper club that they started as kids.
Jessica plays sick to stay home from school. Alice doesn't necessarily believe her but feels bad for everything she's going through and lets her stay home. Liz goes to school and changes clothes so she looks like her twin. She then goes to Veronica and tells her that Mandy is now on her side and thinks she's innocent. Liz "casually" mentions that Mandy would be heartbroken if someone stole her jeweled heart pin before walking away.
Liz then goes to Mandy and lets her in on their new plan. Mandy and Lila don't believe that she's actually Liz until they call the Wakefield house and put both twins through a test. Liz has no clue what the name is of some actor's fiance, and Jessica misspells thief, which makes them realize Liz really is just pretending to be Jess.
Cut to Mandy running up to Liz and accusing her of stealing her pin. They all have a big fight just as Veronica walks up. She lets it slip that she knew someone stole the pin. When they point out that no one else knew it was stolen, Veronica tries to come with a bunch of excuses. The principal shows up and makes her open her locker, where they find everything she stole. She winds up getting suspended.
Steven and Joe, Janet's brother, decide to take an IQ test from some magazine. The results come in saying that Joe has average intelligence but that Steven is a genius. He starts playing chess, reading about law, and listening to opera music. When they watch a Jeopardy type show, he gets all the answers right. Joe goes crazy trying to keep up with him.
While "sick" at home, Jessica helps her mom clean his room and finds a bunch of proof that he lied. She even finds out that he taped the television show and replayed the episode to make him look smart. When she confronts him, he admits that Joe faked the letters to pull a prank on him and that he just played along to drive him nuts.
The Unicorns all show up to kind of apologize to Jessica for thinking that she was a thief. Janet gets Jess alone and tells her what Joe did to Steven. Joe then shows up with a letter he says the testing center sent, which says that Steven got the results of another guy and that he really just has average intelligence. He pretends to be down for a few minutes before announcing that he knew all along Joe was pranking him. Jessica then shows up with the clothes Liz was missing. It turns out that Alice washed the clothes and put them on Liz's dresser, but they fell behind where she couldn't see them.
*Liz is the only one who notices that the first letter from the testing center misspelled quotient. Joe misspells three different words in the next letter. Did his computer not have spell check?
*Anytime some random new girl shows up in a book and something bad starts happening, you know it's her. There was no reason to believe Jess did it.
*Ellen tries to make Jessica pay for her missing earrings. Jessica basically snaps at her and she runs off in tears.
*Elizabeth gets sad because Jessica thinks their snooping club was ridiculous and it's one of her favorite memories.
*Supposedly no one knows Jessica's locker combination except for her. Isn't it funny how Liz constantly gets in her locker in other books?
*I loved the reference to a Watchman! But I also loved that Lila thought she could just get away with watching soap operas on it in the middle of class.