The main character is Michael Webster, a twelve-year-old boy, telling the story from his perspective. He has a crush on Mona Deaton, his classmate. He begins by talking about his sister, Tara, who is always lying and getting him into trouble. Unfortunately, Tara never gets blamed for these things. On his twelfth birthday, Tara ruins everything: she scratches his present, a new bicycle, tells his crush that Mike likes her (as well as opening all of Michael's presents ahead of him, including a CD she says that has great love songs on it), and purposely trips him while he is carrying his birthday cake, resulting in the cake splattering over Michael's face.
A few days later, his father purchases an antique cuckoo clock from a local store called Anthony's Antiques, that is supposed to have one flaw. He had been admiring the clock for fifteen years. It has been said that if a person can figure out the clock's secret, it can be used to go back in time. Tara fools around with the clock, and her father gets very angry. This gives Michael an idea on how to get back at Tara. That night, when the clock strikes midnight, Michael sneaks downstairs and touches the cuckoo's head and twists it around backwards. He hopes this will get Tara in trouble for sure.
Apparently, this little act is the secret to going back in time. Michael wakes up and realizes that it is his 12th birthday all over again. At midnight, he tries to turn the head back to normal, but he realizes that the clock has not been bought yet. He heads back to bed, and wakes up a few days earlier. He remembers the day was when his frog costume for the play "The Frog Prince" gets its zipper stuck. He tries to change events by not going upstairs after walking like a robot up to his room (implying that the events would happen one way or another) then forcing himself to stop and walk back downstairs; however the girls arrive and although he tries to get out of it, they talk him into doing it anyway.
Michael decides this time to lock the door unfortunately he forgets that the lock is broken because it was fixed on his birthday and the girls see him in his underwear just like before. The next day is worse: he has a bad day at school, when he gets beaten to a pulp by star athlete Kevin Flowers, after Tara sneaks Kevin's favorite cap into Michael's backpack. He starts to worry, and tries to tell his family. They trick Michael by saying things and walking backwards. He realizes when Tara calls him a moron [she say norom because they are doing it backwards]. He also realizes that things are going to get worse, and indeed they do: when he wakes up the next morning, he does not notice anything different; however when he walks in the door of his classroom, he realizes the truth: he is back in third grade!Michael finds himself disgusted by how immature his friends are and goes to sleep while thinking that he might be erased for good. But through the next day, he notices he has much more freedom than before and is not being pushed by fate into embarrassment. The next day after that, Michael is in second grade. After Tara pokes him in the eye, he wonders what the pre-Tara years were like since his does not remember much from before age five. That afternoon, he heads over to Anthony's Antiques, only to find it closed. He attempts to break a window with a brick, but his father catches him and takes him home, criticizing him of going on the bus alone, but Michael butters his father up so that he would not be too upset. He tries to talk to his father about the clock and he comments that he has been saving up for years to buy it.
The next day, he wakes up and notices he is back in his old bedroom (now Tara's room). Also, he is five years old, and thus, in kindergarten. He is bored and inattentive, faced with problems such as tying his shoes (and since he still has the brain and mind power of a twelve-year-old, he does it very easily). The next day, he wakes up a year younger, his four year old self is taken to nursery school. He confuses his young friends with his teenage level logic like when he climbs a tree and when they taunt him for being scared, he replies "I'm climbing the stupid tree" and says that means he is not scared, he even goes on to break his arm again as he did in nursery school.
The next morning, Mike wakes up in what he thinks is prison, until he realizes he can barely walk. He soon realizes that he is a baby, wearing a diaper. Unable to escape his crib because of his weakened muscles, and unable to talk properly, he feels trapped. After having a bottle-feeding, a diaper change, and a minute in the baby pen, Michael starts to feel like he will never get to the clock and that this day as a baby might be his last. Even if it isn't, he would be too young to do anything on his last day where logically he'd be a newborn.
His mother takes him to see his "daddy" at work and Michael realizes this is his chance. His parents are heading into Anthony's Antiques. While his parents look for a new kitchen table, he crawls quickly towards the cuckoo clock. Just as it rings for a twelfth time, he grabs the head and twists it forward again, then sets the year dial to 1995, accidentally knocking an unknown year off in the process. In a bright flash of light, Michael is taken back to the morning of his twelfth birthday!
Not quite the present, but close enough, Michael is almost happy to see Tara again, but he can't seem to find her. During his birthday without Tara, his bike isn't scratched, his birthday cake is actually eaten, and Mona's best friend tells Michael that Mona has a crush on him which makes Mona blush. A few days later when the clock is delivered Michael discovers the clock's defect: its year dial is now without 1988 (the year Tara was born), preventing Tara from coming into existence when Michael returned to the present. (Post-2003 reprints of the book replace the year 1988 with 1996.)
However, Michael assures that later he will go back and get Tara, eventually... (though, given the humiliation Tara put Michael through earlier in the book, it can be deduced that Michael will never go back in time to get his sister back).
- R.L. Stine said that this was his favorite book in the series.
- The Cuckoo Clock makes a cameo appearance in The Knight in Screaming Armor. However, when the reader interacts with the clock, they end up becoming the cuckoo bird inside the clock. A different outcome than in the book.
- One choice in Elevator to Nowhere relates to this book.
- Michael and Tara's father was mentioned by name in the book: Herman Webster.
- While in the televised version Michael Webster experience being 12, 6 (on his sixth birthday), and a baby in the past, the book has him experience 12, 3rd grade, 2nd grade, kindergarten, nursery school and being a baby.
- Michael does not experience getting beaten up by Kevin Flowers or being seen in his underwear.
- This is the only single-part episode to not make it to home video.
- Michael's dream is different. It is not of a scary version of his birthday. Instead, it is the clock with Tara's head for a cuckoo chasing him.
- The first time when Michael's father tells Tara not to touch the clock, the father is also visibly more upset than in the book.
- His father is a lot angrier at finding him at Anthony's Antiques than in the book. Later on, when he was brought back to the present, it is the actual present, and he gets the same scolding from his father that Tara got earlier. Michael being happy to see his parents again catches his father off guard.
- Tara's bedroom is his father's office and not Michael's old bedroom.
- Mr. Webster discovers the year 1988 is missing first.
Television Episode Trivia
- One of two television episodes whose opening title appeared in white rather than green. The other one is The Girl Who Cried Monster.
- This television episode failed to get on a VHS.
- The second time Michael goes through his birthday, his mother asks him to help her with his cake. When he goes to her, you see they are outside. But the first time of Michael's birthday, they were inside.
- In the scene where Michael is dreaming, he opens the door to the room the cuckoo clock is in and begins to scream. But we hear the scream a split second, before his mouth opens.
- The first time when Michael's father tells Tara not to touch the clock, you see she has bangs on her forehead. But when she turns around to stick her tongue out at Michael, her bangs are gone.
- This television episode was adapted into Goosebumps Presents Book #2.
- This television episode, along with The Girl Who Cried Monster, on their original premieres had a special opening theme in which there was a ten-second remix when R.L. Stine is walking through the grass with the briefcase. When the G passes the dog, that part of the music is played with a different instrument. There were also different scenes from the television show when the door opened.
- When Michael looks in the mirror at age 6, his scream and facial expression is exactly the same as Macaulay Culkin's scream in the Home Alone movies. He also bears a resemblance to him.
- John White (Michael Webster at 12) played Steve Boswell in Season 2's The Haunted Mask II.
- When Michael is 6, his father reads him Norman Bridwell's "Clifford the Big Red Dog." Like Goosebumps, Clifford is also a Scholastic property.