The novel One Day is a book that people like to give to their friends. Written by David Nicholls, One Day is essentially a love story between two friends, Emma Morley and Dexter Mayhew, which unfolds over the course of 20 years.
So much so, that since its publication in 2009, word of mouth and critical acclaim have led it to be published in 31 countries and become the bestselling British novel of 2010. They meet on July 15 (St Swithin's Day) 1988, during an evening of drunken partying on their final night at Edinburgh University, have a sort of one-night stand and vow to stay in touch.
And so the book does, too, dropping in on their lives every July 15.
It charts their careers – Emma, an idealist with dreams of being a writer, initially struggles in the backwaters, working in a Tex Mex restaurant while composing bad poetry in her spare time, before becoming a teacher and finally a successful writer of children's novels.
Dexter, meanwhile, goes travelling, then falls into tele-vision and finds dubious celebrity presenting vapid youth programmes, but soon spirals into the hinterland of cable gaming shows, relying on drugs and alcohol to prop him up.
And it charts their emotional lives: Emma longs for Dexter but finds herself living with a man she doesn't love, a failed comedian called Ian, while Dexter keeps his feelings for Emma at arm's length and instead moves between conquests before marrying Sylvie, an ice blonde from the Home Counties.
Nicholls describes the book as 'a redemption story.
Probably best known for his first feature film, Julie Taymor's Across the Universe (2007), a musical love story told through Beatles songs, Sturgess could be described as an industry secret, whose career to date has been an intriguing mix of Hollywood (The Other Boleyn Girl and 21) and independent films (Fifty Dead Men Walking and Heartless).
Sturgess hadn't read the book before he auditioned, and thus was unaware of the passion it inspires among its devotees.
'I didn't really think about it at all when we were making the film,' he admits.
'It's only now that people keep asking me how it feels to play such a well-known and loved character that I'm starting to think, "S***, I hope I've been all right." ' We have met in a quiet pub in Camden, north London, on a rather surly June day, when the weather is contradictory enough that Sturgess is wearing a winter coat over a short-sleeve shirt.
He is tall, fine-boned and looks younger than his 30 years.
His good looks are obvious, but with an everyman quality, as Julie Taymor notes during a phone conversation a few days later.