After Carl has been introduced to the class, Mark asks Randall to show Carl what it is like to be a zombie. Carl ends up losing an arm. Mark helps him find a place in Zombietown. The two become good friends since they seem to share similar tastes.
Carl invites Mark to a fishing trip. He pushes Mark overboard, then goes to see Randall and reveals himself actually a human. He said he applied as Randall's roommate two years ago and was devastated when Randall chose Mark instead. He spied on Mark for two years, and disguised as a zombie to get inside Mark's class during the zombie craze. He asks to be Randall's new roommate.
Then Francis Grimes arrives with Mark and arrests Carl for zombie impersonation, which is a more serious charge than attempted murder. It turns out Mark became suspicious when Carl went to sleep which zombies have no need. Randall tells Carl that he chose Mark as his roommate because he thought the "DOI" where Mark works stood for "Dungeon of Intercourse", a sex club in Hell's Kitchen.
Carl is sent to the state prison on Riker's Island.