An avian flu outbreak has killed millions, the nation's infrastructure has crashed and a dirty bomb has destroyed Seattle. Forced to go on the run, Sam awakes to a normal world the next day - and to chaos again the day after that. A single constant between the two worlds will undo all the damage, if he can find it - but that seems impossible. In one world, anything goes. In the other, he's out of danger and sleepwalking through life. So Sam's got an even bigger problem: Which world to choose?