Writing on a day in February when the temperature looks set to reach 18 degrees Centigrade and the sky is a bowl of blue unflicked with a single blob of white, winter seems a long way away. In Jasper Fforde’s new book, Early Riser, winter is a brute: a season of such ferocity that humans have evolved the capacity to hibernate to escape its rigours. It’s a fascinating idea, but one that is also the key weakness of the book. Early Riser has all Fforde’s usual comic genius, spinning word play and world play out of this central conceit, but ultimately the book fails because it’s impossible to construct a world sufficiently similar to our own that Fforde can poke fun at contemporary foibles while still having almost everybody asleep for three months during the arctic winter in Wales. It just doesn’t work. The world, trembling on the brink of toppling into Snowball Earth, with humans that hibernate, would be something completely different, not the hybrid that Fforde creates here. That aside, the story is funny, tense and quite affecting. But where Fforde’s Thursday Next novels and Nursery Crime novels convincingly create worlds that are different yet closely related to our own, this one doesn’t.