The cover artwork features a white birthday cake with blood-red icing. The blue candles on top are giving off a big blaze of fire. A section of the cake had been cut away, revealing that it was filled with all sorts of creepy crawlies. A brown-furred rat is seen gripping the sides of the cake.
Your parents have to go to work on your birthday. They hire a strange entertainer called Dr. MacDeath to throw you a horror-themed birthday party, but he soon proves himself to be evil, and turns one of your friends into a balloon animal. He nails shut all the doors in your house so you can't escape. After an interruption from someone at the door, he forces you to cut your birthday cake, which turns out to be crawling with bugs and worms. You must then decide whether to play party games or open presents.
You play party games, with a choice between Paintball, Dodgeball, Pin the Tail on the Donkey, or a Scavenger Hunt. You have to survive the games and find a way to beat Dr. MacDeath, but he's not exactly playing fair.
You decide to open presents. Your friends' presents have been enchanted by Dr. MacDeath, but he has a few surprises of his own for you.
Side story C
In story B, you open a present Dr. MacDeath gave you, which contains two tickets to a horror-themed amusement park. You take your friend Josh with you and can have fun without MacDeath, but this just leads to two possible endings (one good, one bad.)
List of endings
There are sixteen bad endings and six good endings.
- Non-ending: Dr. MacDeath is revealed to be an insane entertainer who kidnapped the clown your parents originally hired; the clown got free and called the cops so they arrested Dr. MacDeath. Your friends make fun of you and leave. You blow out your candles and wish to have your birthday start over again, but this sends you back to the start of the book.
- You decide to play "Pin the Tail on the Donkey." The cardboard donkey comes to life as a dog with many tails. The dog likes you, but you are smothered to death as it wags its tails in your face.
- During a game of paintball, you're killed when Dr. MacDeath sprays acid all over you.
- While playing paintball with Dr. MacDeath, you switch weapons with him, but whatever was inside his weapon makes him grow to a giant size. He slips on paint and falls over, crushing you and all your friends to death.
- Dr. MacDeath throws a bomb at you, and you dodge, but you're killed in the explosion.
- Dr. MacDeath's bomb turns out to be a stink bomb that is so disgusting that he and all your friends leave the party. You're stuck on your own, and the house still smells terrible.
- Non-ending: You decide to challenge MacDeath and tell him his game isn't fair. The book mocks you for thinking he would care about that, and says that you are too silly to continue with the story.
- During the scavenger hunt you climb out onto a tree branch, which breaks under your weight, apparently killing or seriously injuring you.
- Dr. MacDeath lynches you with the noose you brought back from the scavenger hunt.
- You blow out your candles and wish to be as far away from Dr. MacDeath as possible. Your wish comes true, and you end up in a remote village in an unknown foreign country.
- Dr. MacDeath announces that he has to go to his next party; but promises to "see you tomorrow." When you arrive at school the following day, MacDeath turns out to be your new principal.
- You try to dig up a grave to collect the human bones that you need for the scavenger hunt, but a ghost grabs you and drags you into the grave.
- You're hired at a horror-themed park to re-record all the scream effects, but they do horrible things to scare you so your screams will be real.
- You try to dig up the severed head's body, but it escapes and runs away down the road. So the severed head takes your body instead.
- Your present from Dr. MacDeath turns out to be a box, inside another box, inside another box...You are told that there is no end to the boxes.
- Your friend gives you a birthday present that turns out to contain a stuffed toy wolf. Dr. MacDeath makes it come to life, and it bites your hand off.
- You and your friends cover Dr. MacDeath in paint. This makes him look silly instead of scary, and he's so annoyed that he leaves the party, so you're free to have a paintball war with no parents around.
- Dr. MacDeath turns out to be your friend's uncle, who is just doing everything to prank you for your birthday, not meaning any harm. But the crotchety old lady next door decides your party is getting out of hand, and sends everyone home (with the approval of your parents who had asked her to keep an eye on things.) You are told that this is the best ending in the book, although that's debatable.
- You become Dr. MacDeath's assistant, slowly changing his gross and macabre techniques to acceptable levels, becoming more beloved to the point of replacing him completely.
- You complete the scavenger hunt, forcing Dr. MacDeath to leave. But then another entertainer shows up at your door, so it may not be over yet...
- Josh gets trapped in a ballroom with dancing ghosts. He joined them because he thought it would be "fun" to learn the waltz. You decide he is too dull to be worth saving; and escape on your own.
- You wish on your birthday cake for the severed head to be reunited with his body. The person comes back to life. He is Dr. MacDeath's father, and the two of them planned this so that you would wish for him to be restored to life. As a thank you, he gives you an electric car big enough to drive your friends in.
- The tagline "It's your party, you can scream if you want to!" is a reference to the lyrics of the Lesley Gore song "It's My Party".
- One ending (where a neighbor, who had been asked to keep an eye out for you while your parents are away, breaks up your party and sends everyone home) should be a bad ending, but the reader is told it is the best ending in the book. This is ostensibly because everything turned out to be a birthday prank and you were never in any real danger from Dr. MacDeath.
- Some promotional material referred to Dr. MacDeath as just "Dr. Death." It's possible the name was changed before publication.
- Story A may be considered the "real" storyline of the book, since B is considerably shorter.
- You reach the good ending of Side Story C by abandoning Josh - a change from most books in the series, where you're expected to rescue any friends or siblings you have brought with you (and may get a bad ending as punishment should you try to leave them behind.)