The Forever Story, which launches on 11 August, encourages members of the public to help develop a story online, with TalkTalk donating £1 to TreeHouse for every contribution made.
A long list of famous contributors includes Nick Hornby, Robert Harris, Tom Stoppard and Richard Curtis.
Hornby has penned the opening 35 words of the book: "For the first nineteen years of his life, Johnny Razor wasn't Johnny Razor at all. He was Malcolm Weatherly, and he was born in Mile End Underground station on the night of 17th September 1940."
The story continues with contributions from other authors and CHI staff members. From 11 August, the public can continue the tale in any way they wish. The longer the story, the more money raised.
TalkTalk, the official partner of the TreeHouse since it acquired Onetel in 2005, has a donation target of £50,000.
Hornby, a regular patron of TreeHouse, is also the half brother of Johnny Hornby, a founder of CHI & Partners.