When we meet David Miller, a veteran of the Afghan War, his PTSD from his time deployed has nearly crippled him, with his violent flashbacks continually dragging him back to the most traumatic moments of his tour. However, when David crosses paths with a shadowy organization called Fallen Arrow, it's revealed to him that his flashbacks aren't memories, but, in fact, a form of time travel. After exhaustive and reality-warping training, David is successfully turned into a fully deployable time agent.