Finding himself 700 years in the future, Sixteen-year-old Marcus Anderson slowly wraps his head around the idea that he's now a Guardian, a soldier infused with the Light of the mysterious Traveler. As he does so, he meets a friend from his past, and her Exo creation. The rookies soon join millions of others, discovering the secrets of their galaxy, and the threats that plague it.

He had no hope of rescue until he came across a lone Titan, her pilot killed in action. She had no hope of survival until he happened upon her. They met as foes, but fate made them friends. Now, they've uncovered something that could destroy everything that the frontier has worked to build. They must face the inferno of war together if they are to survive.