Saul Dawson-Smith can memorise the sequence of a shuffled deck of cards in under a minute; he can recite pi to a thousand decimal places and he remembers every conversation he's ever had. He is ten years old.
Howard McNamee is twenty-eight: lonely, overweight and poorly-educated. He lives in the north of England, far from the scene of his difficult Glasgow childhood, in the home he shared with his mother before she died. Struggling to pay his rent with a succession of menial jobs, Howard comes home each day and talks to the late Mrs McNamee, as he sits in front of the wardrobe that still contains her clothes.
Through a series of unexpected events, these two solitary people find themselves forming an unlikely friendship, as Howard is taken under the wing of Saul's parents, thrust into a life in London (where he makes new friends, tries to navigate a bewildering new city, and accidentally acquires a Russian internet fiancee) and Saul prepares himself for the World Memory Championships - the event he has been training for his whole life.
But as the pressure mounts on the little boy, and his well-meaning but single-minded parents grow increasingly less able to see beyond their own ambitions for their son, Howard realises he must act to save his small friend from a life of soul-destroying competitions and unbearable expectation. The decision he reaches turns all of their lives upside-down.
Saul and Howard embark on an extraordinary adventure: seen by the world as an apparent abduction, the road trip they take together is at once an exhilarating escape-bid, a journey into Howard's own past and a bewitchingly strange voyage of discovery for man and boy.