Foolhardy police officer Brian Nightraider is dismissed from the force for a history of reckless behavior that ultimately resulted in his partner's death. While wallowing in self-pity, the disgraced officer receives a curious invitation from the United Nations Immigration Bureau Special Investigation Unit. He has been recruited to join the Marginal Service, a secret underground branch of the UN tasked with handling Borderlanders.

Indistinguishable from humans, Borderlanders are aliens that peacefully coexist in society. But now, a Borderlander terrorist organization has emerged, manufacturing and distributing a potent drug called Confu. With the Borderlanders' ability to regenerate and blend in as humans, uncovering the drug-trafficking ring will be no easy undertaking. However, the ragtag group at the Marginal Service are not one to back down from a challenge—even as their work exposes some unexpected figures as Borderlanders.