Mark chooses April Fool's Day to ask Callie to take their relationship to the next level, but his romantic gesture is threatened when Callie's vengeful ex-boyfriend returns to win her back. Meanwhile, Leonard tries desperately to redeem a winning lottery ticket as Randall attempts to cut himself in on the prize.
When the country's biggest pop star ("Lady Hoo-Ha") goes zombie, millions of her devoted fans follow suit. When Mark befriends one of the new zombies, Randall is forced to deal with his jealousy issues.
Mark becomes conflicted about his relationship with Callie after she gets a promotion by turning herself into a man. He does his best to be understanding, but their love is soon put to the test when they are asked to embark on a dangerous mission to the fabled underwater city of Atlantis.
In honor of Twayne's 10-year anniversary of running the D.O.I., Callie and the crew throw him a Roast. But when Mark's attempt at edgy humor goes too far, Twayne quits, leaving Mark in charge. Before his first day as boss is up, Mark makes a management mistake so catastrophic that it almost destroys New York City.