The guardians, the shadowy heroes of the top-secret program designed to protect members of the most elite government organizations, are being hunted down one by one. There is a single explanation: a traitor must be embedded somewhere in their midst. But if they themselves are the target, who will protect them?

CIA operative Renee Niezen has heard tales of the guardians, though she's never really believed in their existence—until she is approached by Charlotte, an old friend who desperately needs her help to stop the systematic destruction of the guardian program. Renee accepts the plea for assistance, but not everyone is thrilled to have her on the team. Kade—one of the last guardians standing—is unimpressed with Renee's qualifications and turns instead to the legendary Saint Squad for help. But when Renee is caught in the crosshairs, Kade must set aside his antagonism for the woman in order to protect her. Their grudging alliance soon develops into much more—but before the pair can examine their feelings, their investigation takes a dramatic twist. With lives on the line, Renee and Kade must use their spy training at every turn as they draw dangerously close to the shocking truth.