One morning, Pooh wakes up at “sixteen o’clock”. As he gets out of bed, he slips on his bag of marbles and skids across the floor. Then Piglet enters through the door and slips on the marbles too, and they both crash into the wall. When Pooh straightens up, he gets poked by “a marble that looks very much like a tooth.” (It actually is a tooth.) He and Piglet wonder where it came from. They decide to go to Rabbit's house to see if he can help.
Rabbit examines the tooth and states that it's Pooh’s sweet tooth and since it's out of Pooh's mouth, because Pooh hasn’t eaten any honey since he found the tooth. Furthermore, until Pooh gets the tooth back, he is restricted from honey, which of course horrifies Pooh. But Rabbit realises that there's only one thing for it.
He attempts to tie the tooth back to Pooh’s mouth, but actually ties a string attached by a tooth to his snout. Then, Rabbit takes it to his garden and plants it next to some sweet potatoes and sweet peas. Apparently, Gopher has been digging under Rabbit's garden again, causing Rabbit, Pooh and Piglet to fall into Gopher's tunnels.
Rabbit starts to lose his temper about Gopher digging under his garden, until the latter angrily confronts him. The tooth is lost inside Gopher's tunnels. As Gopher and the others enter his workshop, he discovers that it has been prowled through by a gang of robbers called the Pack Rats, who took things from Gopher’s workshop (including the tooth) to switch them with walnuts.
Meanwhile, the Pack Rats are making their way through the 100 Acre Wood, and try to take a sundial. Owl comes to them and talks about yet another member of his family and takes the pretty "doorbell." While Pooh tries to retrieve the tooth from Owl's house, Rabbit stuffs Piglet into the Pack Rats' sack in case the tooth is in there. Not only do the Pack Rats snatch the tooth from Owl's door rope before Pooh can, it results in them snatching Piglet (still in their sack) as well! Pooh and his friends race after them.
In their lair, the Pack Rats are surprised to discover Piglet in their sack, so they stuff him in the armor of a knight. Then, they try to place Pooh's tooth in their chattering Tooth toy, but to their disappointment, it's too small.
Pooh, Rabbit and Gopher hear Piglet's cries for help, and come to his rescue. And soon, Gopher gets Piglet out of the knight and they are upset that they can't seem to find the tooth. The Pack Rats come out of hiding and they want Pooh's watch, after catching a glimpse of it. Pooh says he'll trade it for his tooth. The Pack rats huddle and then say that if Pooh can guess where his tooth is, he can have it. Pooh says the last place he would look is behind the Pack rat Leader's back because that would be cheating, and that's just where it is! The Rats, knowing that Pooh won the guess, reluctantly hand the tooth over to Pooh.
That evening, Pooh tells his story to Christopher Robin. Christopher tells him that Pooh bears don't have teeth and if they did, Pooh's sweet all over! He tells Pooh that the tooth is a baby tooth he hid with his marbles. He gives it to Pooh and the next morning, Tooth Fairy gives Pooh a pot of honey - much better than walnuts!