|“||I've come here to create a new country for you called chaos and a new government called anarchy. All for you.||„|
|~ Gaerity, in a phone call to Jimmy Dove|
Gaerity is an Irish terrorist and the former friend of Jimmy Dove, whose true name is Liam McGivney. Previously, Gaerity and Jimmy had been members of the Norther Ireland terrorist cell. However, when Gaerity attempted to trigger a bomb that would've resulted in civilian casualties, Jimmy turned on him, resulting in the death of Gaerity's sister and Jimmy's girlfriend. Gaerity was imprisoned as a result.
Years later, Gaerity managed to escape his confinement in Northern Ireand, killing his cellmate and a guard in the process. Seeking vengeance against Jimmy for his betrayal, Gaerity journeys to Boston, where Jimmy is a retiring bomb squad veteran. Taking residence in an abandoned casino boat, Gaerity becomes a janitor at the police department to learn more about Jimmy's new life. Gaerity proceeds to kill members of the bomb squad by using bombs designed specifically to kill defusers. Gaerity goes on to kill Jimmy's pet dog and displays the body for Jimmy to find.
Dove's uncle, Max, attempts to stop Gaerity himself at a bar, but is captured instead. Gaerity latches Max into a makeshift bomb, intended to kill both Max and Jimmy when he attempts to defuse it. However, Max activates the bomb, sacrificing himself to save Jimmy.
Jimmy manages to track Gaerity to the abandoned ship, where Gaerity reveals that he has planted a bomb in Jimmy's wife Kate's car, planning to kill both his wife and daughter. Before Jimmy can stop him, Gaerity activates the arming mechanism and battles Jimmy throughout the ship, which is rigged to explode. Eventually, Gaerity handcuffs himself to Jimmy, intending for both of them to die in the doomed ship. However, rookie technician Anthony Franklin, who had deduced Jimmy's past, arrives and rescues Jimmy. The two then escape, abandoning Gaerity and leaving him to perish in the explosion.