It's been like a whole year since Nancy tried to kill her sister and got sent to an institution, so of course she's ready to come home again. Emily starts out the book thinking about what happened over the last year and watching her stepsister Jessie move her things into her room so Nancy can have a room of her own. While holding a swan that someone gave Jessie after her mother died, Emily hears a scream that causes her to jump and break the swan.
The scream came from Rich, her younger stepbrother. He got really dark over the last year and now spends all of his time working on a horror movie with his friends. Rich is pissed off because someone told their dad that he sneaked out and went to a party, which ended with him getting grounded for six weeks. Both deny him getting in trouble, but he doesn't believe them.
Jessie's friend Cora-Anne comes over, forgetting that Nancy is coming home. She helps diffuse Rich by talking to him about horror movies. They hear their parents coming in, and Nancy shows up with a knife in her hand. It turns out that it was a prop leftover from Rich's film. She seems okay but also really nervous and shy. After just a few minutes, she makes up an excuse and goes to her room.
Emily does find a bottle of expensive perfume in her room tipped over. She immediately blames Nancy and plans to talk to her before Cora-Ann interrupts. She points out that it was probably just the breeze from the window Emily left open and that she needs to calm down. Rich makes a rude comment about the smell and makes it clear that maybe he was the one who knocked it over.
They all go out to breakfast today to spend some time together. Nancy then suggests that she and Emily talk, but when they're alone, she tries to strangle her. Ha, just kidding! She actually just puts her hands on her neck to show that Emily doesn't really trust her. Trying to kill someone really damages the trust they have in you! Emily's little dog Butchie comes running in and jumps all over Nancy. That breaks up the moment and lets them relax enough to talk about what happened. Emily then goes out with her boyfriend Josh, but when she comes home that night, she hears someone sneaking around the house and thinks it might be Nancy going crazy again.
Cora-Ann has been hanging around the house a lot because her parents are fighting. She admits to Emily that her dad moved out and that she didn't want to bother Jessie with her problems. Jessie then gets pissed and tells Emily that Cora-Ann is her friend and her friend alone. She wakes up a few nights later because of a bad nightmare. She had a friend named Jolie at camp who died, and she found her body. The nightmares all came back in recent months, which as Emily points out might be because Cora-Ann looks an awfully lot like her.
Then a bunch of weird things happen. She finds that someone sliced her favorite black dress in half. She blames Nancy, and Cora-Ann thinks it was the cleaner. Rich shows up with a pair of scissors and jokes about it. She tells her parents, but they think it was just a joke. It doesn't help that Nancy puts her foot out and trips her, causing Emily to fall down the stairs. Nancy swears that it was an accident and that her medication causes muscles twitches. She does have a nice moment with Nancy, who is working on fixing up their old tree house. But then someone cuts her brakes.
Emily ends up in a bad accident and remembers seeing her sister carrying a toolbox. She tells her parents, but her stepdad blames himself. He knew the brakes were loose and just never got around to getting them fixed. Emily finally tells them that when Nancy really does kill her, they should probably ground her for a few weeks.
A few nights later, Cora-Anne shows up with her bag in the middle of the night. Her dad came by the house and they had a huge fight. They offer to let her spend the night with them. When Emily gets up the next day, the other girls tell her to use the bathroom first. Emily notices that the toothpaste feels weird and then she can't open her mouth. When she looks over, she sees a tube of super glue in the trash. Um, super glue doesn't work like that?
Cora-Ann helps her rinse her mouth and calls 911, who tell them to get her to the emergency room. She naturally blames Nancy, and Nancy bursts into tears, freaks out, and runs from the room as she cries about people always blaming her for stuff. Gee, I wonder why they would do that. It probably doesn't help when Emily finds her dog murdered on the floor, and Rich makes a rude joke about dead dogs in the house.
To get her mind off all the stuff at home, Emily asks Cora-Ann about her family life. Cora-Ann tells her that her mom wants to move them all back to Parkerstown. Turns out that's the same town Jolie came from, and she lets it slip that she knows what happened. Jessie is suspicious because she never told her "best friend" about one of the most important events in her life. She convinces Emily to go with her to her friend's house. They see Jolie's parents on the porch. They tell her that Cora-Ann was Jolie's cousin, the same cousin who was so upset over her death that she couldn't come to the funeral.
Jessie decides that Cora-Ann is responsible for everything. She wore that black dress, used Emily's perfume, and the dog always came to her first. It's clear that Cora-Ann did everything to hurt Jessie and that it had nothing to do with Emily. Emily immediately apologizes to Nancy, but Nancy won't let her in her room. She says she's too busy working on a mural she's painting in her room. A mural that she won't let a single person see.
Cora-Ann calls to talk to Jessie, who blurts out that they know everything about who she is and what she did. Right as she goes to say something else, a storm that suddenly picked up knocks out the phone line. While searching the house for candles, Cora-Ann shows up at the door with a big ass knife in her hand. Jessie runs for the phone before remembering that it's out, and when she turns around, her friend is gone.
Cora-Ann somehow gets in the house and comes at them with the knife, but Nancy shows up and slams her over the head with a frying pan. I cannot make this crap up. Jessie starts gushing about how she saved her, and Nancy smacks her over the head with the same pan. Nancy then turns on Emily and admits that she never really recovered. She still had the same knife from before and kept it in her bag. Cora-Ann found the knife when she accidentally took the bag and was coming back to tell them. I guess she was in shock, which is why she never said a single word.
Emily goes running through the house and winds up in Nancy's room. She rips the sheet off her mural and sees that it's just the word "hate" repeated over and over again. Nancy attacks her, Emily says she forgives her and tries to keep her calm, and they end up hugging it out. Their parents come home to find two passed out girls on the floor and the other two hugging.
Nancy goes back to the institution at the end. Cora-Ann's parents went to a therapist who told them to get a divorce. They seem a lot happier and her mom wants to stay in Shadyside. She admits that she became friends with Jessie for revenge but later realized she didn't kill her cousin and just became her friend. Their parents call Rich to the table for dinner, and he says he's waiting for this show to end. What is he watching? Family Feud. Ha, ha?