December 1348. With the country in the grip of the Black Death, brothers John and William fear that they will shortly die and go to Hell. But as the end draws near, they are given an unexpected choice: either to go home and spend their last six days in their familiar world, or to search for salvation across the forthcoming centuries – living each one of their remaining days ninety-nine years after the last. John and William choose the future and as they find themselves in stranger and stranger times, the reader travels with them. But their time is running out – can they do something to redeem themselves before the six days are up?