Harrison travels to New York to meet with Quinn, a mysterious avant garde artist, who's offered Harrison the chance to buy one of his rare, much-sought-after works of art. During their initial meeting, Quinn presents Harrison with a bracelet and reveals himself to be half-alien, half-human mutant left behind during the 1953 invasion.
In addition, Quinn tells Harrison of his plans to dissolve the alien Advocacy and declare himself supreme leader of the planet Earth. Part of his plan requires Harrison to convince the United Nations to eliminate most of the world's human population to permit alien occupancy and domination. He also explains that he is in hiding from the other aliens, who want to experiment on his body so they can learn how to develop an immunity to earth bacteria.
When Harrison scoffs at Quinn's ideas, the artist activates Harrison's bracelet, turning it into a torturous shackle. Just then, aliens disguised as police officers trace Quinn to his hideaway, forcing him and Harrison to flee through a trap door, which leads to the bowels of the New York City subway system.
Meanwhile, Ironhorse and Suzanne arrive in New York and trace Harrison to Quinn's apartment. There, they find a matchbook cover which Harrison has marked in a secret code, identifying Quinn as an alien. The true horror sets in when Ironhorse and Suzanne realize that Harrison may now be an alien!
While Quinn and Harrison race through the underground tunnels intent on getting to the United Nations, the aliens are in hot pursuit. The invaders corner them in a U.N. conference room, while nearby, Ironhorse and Suzanne arrive in the hopes of intercepting Harrison and determining his allegiance.
In the ensuing battle, police officers enlisted by Ironhorse turn out to be aliens and, in the confusion, Quinn escapes, leaving Harrison behind. A wary Ironhorse approaches him with his gun drawn. Luckily, Harrison tips his hand with one of his endearing quirks and makes it clear that he has not joined the alien causes.