Regan Fitz and Elliot Mason are training to become Glitchers, or time travelers who prevent others from altering important historical events. They've always been enemies-but everything changes when they find a letter from the future that warns of a devastating event to come. Suddenly forced to work together, Regan and Elliot must get over their animosity fast, because to save everyone they know, they'll need to break every rule they've ever been taught. .