Just how much of a "discovery" it is, though, seems to be in dispute. "The book was recently discovered and brought to the attention of the Plath Estate," said Ros Edwards, of Faber's rights department. "They decided the book was worth publishing, and we were delighted to be involved."
Becky Cape of the Lilly Library, by contrast, said: "It's been known about for years. At least 200 people have looked at it. It's listed in the catalogue."
Plath wrote two books for children. The other, The Bed Book, was published by Faber & Faber in 1976 and is still in print. Like The Bed Book, The It Doesn't Matter Suit was written in 1959, but it has languished in the archives ever since.
A charming, light-hearted fable, it features the adventures of little Max Nix in the village of Winkelburg, as he hunts, fishes, skis and milks the cow in his all-purpose yellow suit.
It was written while Plath was living in Boston with Ted Hughes. On 6 October 1959, however, Plath's journal despondently records the rejection of "Max Nix", and no more is heard of it. After her death the typescript was swept up among a heap of papers and memorabilia, photos and correspondence and sold to the Lilly Library by her family.
The book was such a hit at the Bologna book fair that Faber had to organise a series of auctions for the European rights, with four or five publishers in each country competing. It is coming out in eight foreign editions.