Based on the Dark Horse comics, Resident Alien follows a crash-landed alien named Harry and his life on planet Earth. Harry and his baby Bridget are stuck in prison on the Grey Moonbase, while a shape-shifting Alien called a Mantid has taken over his body on Earth passing himself off as the real Harry Vanderspeigle. Harry manages to escape the Greys and arrives back on Earth for a showdown with the Mantid Alien, but soon finds he may not have what he needs to finish the job.