The Drake twins have been locked away forever, and the trauma they caused is preparing to heal, but that only leads to older wounds being reopened.

Frederick comes to Lesley, Malcolm, and Julian with a problem: the agents of MI6 seem to be under siege by an unknown ailment. Strange, erratic behavior, fights breaking out without any source. Determined, they set about investigating, but nothing is as it seems.

The crew is joined by a face from Malcolm's past, which only further aggravates the situation. Before too long, Malcolm starts exhibiting the same weird behavior that the agents did. All at once, the case goes from objective to deeply personal. With Malcolm ostensibly out of commission and under siege himself, Lesley and Julian must find a cure, or risk having to keep him locked up forever.

What they discover, both about themselves and each other, is not what they expect. And it is certainly not what they are prepared for.