When an asteroid strike causes a major disaster in Boston, it forces physicist Ben Shore to rethink his life and purpose. Together with his step-sister and mathematics whiz, Nicky, and orphaned early-teen hacker, Jessie, he embarks on a quest to find a way to avert similar or worse disasters from happening. Ben's attempts to create a new physics change their world forever and turn their basic assumptions about reality on their head.
But they only realize just how little they understand the full implications of their work, when Frank, Ben's former collaborator, has Ben kidnapped in order to force him to reveal what Ben has secretly been working on. Frank's action brings unexpected visitors from two different times of the future into the present.
Now they all need to work together to ensure that the future they know actually comes into existence, while at the same time avoiding the paradoxes that the multiverse and time travel produce, and which may destroy everything they are hoping to achieve—and quite possibly tear their families apart.
Tomorrow's Yesterdays is about love, family, personhood, artificial intelligence, time, the multiverse, and the true meaning of 'and'.