What would happen if, in the middle of a contented middle-aged life, your seventeen-year-old self suddenly appeared? And what if he said you had done everything wrong?

But there's still hope because he's come to help. He's going to show you how to live the rest of your life the right way. Confusing enough? Almost simultaneously you're catapulted forward to the last day of your life. And after seeing how you end, you're brought right back to today – and that seventeen-year-old you.

Worse, someone not of this earth shows you very clearly that the fate of the universe could well be determined by what you decide to do next.