The 13-Storey Treehouse

The book begins with the narrator and fictional depiction of the author, Andy Griffiths, giving an introduction to himself, his friend and illustrator Terry Denton, and their treehouse.

Andy wakes up one morning, and on his way to getting breakfast, he meets Terry, painting a white cat yellow to turn it into a canary, or a "catnary". After being dropped from the treehouse, the cat grows wings and flies away. Andy and Terry are then greeted by their animal-loving friend Jill, who wants to find her pet cat, Silky. It turns out that the cat Terry painted was that exact cat. Andy and Terry try to remain innocent when Jill questions them. Right after Jill leaves, Andy and Terry receive a call via a 3D video phone by their publisher, Mr Big Nose, who is upset that the duo is behind schedule.

They soon try to come up with ideas for a book, but Terry only has a few self-portraits of his finger. Since they're Terry's only pictures in his folder, he and Andy end up in an argument which starts a drawing competition. Once they compete for the best banana drawing, Andy gets upset and gets in a fight with Terry, armed with the Giant Banana Terry grew in the intro. Terry ends up knocking Andy out and pours a bucket of water to save him. They come back to ideas for their book, and it turns out that Andy has four pages that read "Once upon a time". But before anyone can say more, Terry gets distracted by television as his favorite show, Barky the Barking Dog, is airing. Andy is not amused at all and throws the TV out.

Right afterwards, the duo are greeted by Bill the Postman, who is giving them sea-monkeys that Terry ordered. Andy is very unhappy with this. Terry goes down to the Secret Underground Laboratory to hatch the sea monkeys. After Andy waits for a long time for him to come back, he goes down to the Secret Laboratory. Andy gets even more bored and angry while Terry finishes hatching a sea-monkey. He then starts feeding it, but it grows into a mermaid named Mermaidia whom the duo put in a bathtub. She and Terry grow attached, leaving Andy alone. He overhears the love conversation from the bath door, which ends in Terry kissing Mermaidia. Once Terry runs off, Andy enters the bathroom and finds out that Mermaidia was a sea monster in disguise. Andy records her singing a song about how disgusting she is. He runs down the stairs to find Terry, who is eating marshmallows. After being shown the proof that Mermaidia is a monster, Terry sides with Andy, and questions on what to do. They end up going to the underground laboratory so they can shrink her down with the banana enlarger.

Later, the duo began to work on their book, but Terry was too sad to concentrate. Andy then gets Terry popcorn and lemonade to cheer him up. Terry additionally got himself bubblegum. He burps a bubble which he had trap himself. Terry floats away and Andy does a golf swing which successfully saved him.

Then, Terry gets an idea of a book about a superfinger. So they wrote and illustrated it. Terry gets distracted by a package, which contained the real sea monkeys, he then goes to the lab to make the sea monkeys. However the sea monkeys were causing chaos. Terry grabs the Giant Banana and whacks the flying object out of the tree. Then the duo launched the monkeys and the Giant Banana far away with a catapult.

When Andy and Terry began to write their book, a giant gorilla started shaking the tree yelling, “BANANA!” Then a chauffer arrives, informing Terry has won the Barky the Barking Dog drawing competition and gets to meet Barky. But squished by the giant gorilla.As the duo loses hope. 13 flying cats, lead by Silky, began fighting the gorilla. Which was successful. The canaries then lift the gorilla away.

A doorbell rings, however the duo discovered it was Jill, in which she thought she saw Silky. Andy confessed that it was Silky but Terry turned her into a canary. But Jill was glad and thanks Terry.

However, Andy is still upset with how he and Terry haven't got their book done, but Terry suggests that they write what happened that day. They write the events up and with the help of Jill in a Santa-like sleigh, get their book to Mr Big Nose for it to be published.

The book has spawned a series of sequels, each of them adding 13 stories to the treehouse and other humour fiction:

• The 26-storey Treehouse (released in September 2012)
• The 39-storey Treehouse (released in September 2013)
• The 52-storey Treehouse (released in September 2014)
• The 65-storey Treehouse (released in August 2015)
• The 78-storey Treehouse (released in August 2016)
• The 91-storey Treehouse (released in August 2017)
• The 104-storey Treehouse (released in July 2018)
• The 117-storey Treehouse (released in July 2019)
• The 130-storey Treehouse (released in October 2020)
• The 143-storey Treehouse (released in October 2021)
• The 156-storey Treehouse (released in September 2022)
• The 169-storey Treehouse (released in September 2023)
• Treehouse Tales (released in March 2022)
• The Treehouse Fun Book 1 (released in March 2016)
• The Treehouse Fun Book 2 (released in July 2018)
• The Treehouse Fun Book 3 (released in April 2019)
• The Treehouse Joke Book (released in September 2019)
• The Treehouse Joke Book 2 (released in May 2021)
• The Bumper Treehouse Fun Book (released in December 2021)

• At the start of the second paragraph, Mr Big Nose will call Andy and Terry to tell them the deadline of their next book as pointed out in The 39-storey Treehouse.
• At the end of each book, they will show the previous pages.
• The animals are frequent characters appearing mostly for comedic effect.