The outcasts of time / Ian Mortimer.

The year is 1348 and brothers John and William have been infected by the plague. Their fate is sealed. Until a voice from the skies offers them a choice: 'You may stay here and return to your house, and spend your last six days with your wife and children. Or you may put yourself in my hands now. I will wipe the scars from your face and the swellings from your body. I will extinguish your fever. I will let you live your last six days in the distance of the future.' John and William agree: they will live for six more days and in return they will do good deeds in order to try to save their souls. But there's a twist: each of those six days will begin ninety-nine years after the last. As they travel through time, the reader travels with them, seeing the world change through conflict, disease, progress and enlightenment. But time is running out - can they save their souls before their six days are up?