New York City is gearing up to celebrate Treegasm, the beloved mating ritual of a bizarre tree race, when Mark is unexpectedly tasked with handling the event. Unfortunately, one of the two trees is getting cold feet, terrified of a monogamous lifestyle. Mark must deal with the repercussions of this decision while fending off advances from Callie, who is undergoing her own strange transformation. In the meanwhile, Randall finds out that he has lost something very precious to him. Specifically, his penis.
After an unidentified pile of goo goes on a rampage, Mark leaves Leonard in charge of figuring out the creature's origin. Taking advantage of Mark's day off, Randall takes him on a road trip to south Jersey, where Mark discovers that his roommate has not "come out" to his parents as a zombie. As Leonard tries to assimilate his formless new charge into city life, Mark struggles to keep Randall's secret from his rabidly anti-zombie family.
When Grimes busts an unregistered demon trying to sell hellspawn to a barren couple, Mark is forced to assume possession of the baby until it can be turned over to a local orphanage. Seeing Mark with the baby stirs up new emotions in Callie, and she unexpectedly goes into heat (taking Twayne along with her). As Twayne learns the ins-and-outs of demon mating, Callie must make a decision between single life and spawning soldiers for Satan's dark army.
Mark Lilly, a social worker at New York's Department of Integration, is having a rough day. His department has been slashed, his zombie roommate has lost a chin, and his only remaining co-worker is a drunken wizard. On top of that, his demon girlfriend wants Mark to meet her father in Hell... literally. Can Mark do the work of 20 people and still manage a social life, or will his crazy schedule lead to unforeseen consequences for one of his case files?