The Coffin starts out with some random crazy guy (or gal?) talking to himself. He keeps mentioning that he hates the dark and hates being kept away. I think I'll just stick with he from right now because I'm not even sure how many chicks are in this book! It then jumps to some random housekeeper named Mavis cleaning up at work when someone grabs her from behind and kills her.
Then we get introduced to Tanner, the main character of the book. Tanner lives with her dad because he's a professor at Salem University, which means she gets free tuition. After her parents divorced, she moved in with her dad. Her dad is incredibly strict and mean, while her mom is wild and crazy. Her dad also teaches psychology, and most of her friends took his class and did really bad.
She thinks about how her dad has this fancy music room because he plays 11 instruments, while she only plays one. She hates the room so much that she rarely goes in there. Her friends all try convincing her that she should throw a big party because her dad is out of town. Tanner kind of agrees but not really.
When she gets home, she finds the house empty even though her housekeeper Silly should be there. Tanner finds a big chocolate cake with a piece gone and a note from Silly saying she left her ice cream signed with her real name of Mavis. Duh du duh duh. Tanner gets a little upset because Silly didn't leave her dinner so poor her has to make her own sandwich.
While wandering around the house, she finds Silly's purse on the couch. Thinking she went to the dentist because she complained multiple times about a bad tooth, she locates the dentist and calls him, but she isn't there. Someone appears out of nowhere, throws a bag over her head, and knocks her out.
Tanner wakes up locked in the music room with a dude in a Halloween mask sitting across from her. He makes her write a note that says she decided to leave town and go with her mother on a trip to the Orient. He makes a bunch of vague and threatening statements about her, and lets her know that her friends will believe her note because he's leaving it on the mailbox. When he leaves, he casually mentions that he killed her housekeeper.
Tanner's boyfriend Charlie calls her friends Jodie and Sandy because he tried calling her and no one answers. Sandy mopes around about how she wishes she had a guy like Charlie, while Jodie tries to get him calmed down. He goes over to her house and finds the note, and she sees everything because apparently her dad has security cameras set up so he can keep an eye on things outside.
Tanner gets all mopey about how she can't put on socks or get a snack, but she still manages to get some sleep. The guy shows up the next day with a bunch of wood, nails, and a hammer, and he starts making a huge box. He demands that she get in it, and when she doesn't, he picks her up by her hair and throws her in it. He puts the lid on, nails it in place, and leaves her.
When he comes back, he lets her out of the box and suggests she eat something. They head into the kitchen, but when he mentions ice cream, she finally realizes that he killed Silly. It probably helps that she sees her scarf hanging out from the lid of the freezer. Dude tells her to open the freezer, she refuses, he tells her to do it again, shoves her into the freezer, and when she sees Silly's body, she passes out.
Charlie talks to his friend Vince who conveniently knows all about Silly and where she lives. He decides to go to Tanner's house and look for clues, but he hears a noise in the background. A motorcycle comes out of nowhere and knocks him down. Vince, their friend Phillip, Jodie, and Sandy all see him in the hospital, and he keeps moaning about Tanner.
Cut to Tanner back in the music room. The guy comes back and makes 957 comments about how he knows her dad. Turns out that her dad knew the dude was crazy and tried to help him. He keeps putting her in the "coffin" and taking her out before leaving again. She tries to get help by hurling lamps and other things at the windows in the room, but her dad used shatter-proof glass.
Tanner sees the ambulance lights and gets close enough to the windows, which are like eight feet off the ground, to see what's going on. She screams and cries, but no one can hear her because the room is soundproof. Oh, and she cries for pages and pages about Silly. The guy comes back, lectures her on making a mess, puts her in the coffin, and lets her out again.
Jodie goes back to the house and realizes that if Tanner really left, she'd take a lot of stuff, but there's nothing missing from her room. After some thought, she wonders if Tanner fell asleep in the music room and accidentally locked herself in the room. She writes a note and slips it under the door, and Tanner responds. She promises to get her best friend out, but then the guy pops up behind her.
The next time the guy tosses her in the coffin, Tanner realizes he did a really shitty job of putting it together and she can actually feel some of the nails coming loose. She starts slowly pulling the nails out with her hands and feet, doing even more damage to her poor feet, which she screwed up by walking on the broken glass from the lamp. She gets enough out that she can create an opening in the back that she can squeeze through.
Charlie keeps calling the hotel where her dad is, but he is never in his room. He does finally get in touch with him, and the professor tells him about one student that he had institutionalized. The kid got out when his insurance was up, and he's back at Salem. Tanner's dad finally realizes that something is wrong, but Charlie lies to him. He talks to a cop, and the cop goes over to her house. He doesn't think anything is wrong even though he finds the back door unlocked and standing open.
The guy comes back to the music room, Tanner slips out, and waits for him to open the coffin lid. When he does, she rushes out and slams the lid on him except that she realizes he has the only key to unlock the music room door. She manages to get her hand inside the coffin enough to get out the keys.
Right when she reaches the door, she turns and sees Phillip. See, this is what I hate about the Nightmare Hall books: the villain is always someone who is barely in the book. I think Phillip is only mentioned twice, but suddenly, Tanner thinks about how if she didn't start dating Charlie, she probably wound have ended up with Phillip. She gets to the door and manages to get out and lock it from the other side.
The book ends with the gang sitting around in the hospital. Jodie was safely found in the basement because Phillip could apparently kill the housekeeper but no one else. Someone mentions seeing him on a motorcycle that he borrowed from the garage where he worked on the day someone hit Charlie, and they all think it's sad. Then, they all joke about Tanner throwing a party because Salem is apparently close enough to Sweet Valley that after almost dying, you should tots have a party!