"Are you happy?" That's the last thing Jason Dessen hears before a masked man knocks him out. When he regains consciousness, a stranger greets him with the words: "Welcome back, old friend." But Jason has not returned to his own life; instead, he finds himself in a life that could have been. Without his beloved wife, without his son, but at the peak of a brilliant career as a scientist. But is this all real? Faced with a choice – what does he truly want from life: love or success? A journey as dangerous as it is breathtaking through space and time begins...