Stranded on a parallel Earth, the Tenth Doctor finds himself mentoring a traumatized child soldier enlisted in a hopeless war to save humanity. With an endless number of mysteries in sight -- from the enigmatic alien invaders they call Angels, to the strange machines known as Evangelions used in the planet's defense, to the shadowy maneuvers of those in power -- the Doctor is drawn deeper and deeper into a web of mistakes and sins that threaten to consume all humankind. In time, he'll face the darkest question of them all: what if there are some worlds -- and some children -- even the Doctor can't save?

Hadley Jamison doesn't know what to think when she hears that her classmate, Archer Morales, committed suicide. She didn't exactly know him, but that doesn't stop her from feeling like there was something she could have done to help him. So to Hadley's surprise, on the very night of Archer's funeral, she has a run in with Death himself and is offered the chance to go back in time to stop Archer from ending his life. The catch? She only has twenty-seven days to do it. And if Hadley doesn't succeed? Well, she doesn't want to think about that.