Based on Gerry Dee's real-life experiences as a high school teacher before he switched to comedy full-time, Mr. D is a story about a charming, under-qualified teacher trying to fake his way through a teaching job, just like he often fakes his way through life. The premise shines the light on teaching from the teacher's point of view, and as it turns out, teachers don't know everything, especially Mr. D—who struggles to keep one step ahead of his students.
Gerry is forced to sub at a tough inner-city school after losing his job at Xavier Academy. Back at Xavier, the staff is worried that Robert is having a nervous breakdown because he didn't get the principal's job.
Gerry is assigned an educational assistant, Marty, who quickly becomes a new source of irritation in the classroom
When Lisa asks Gerry to cover coaching duties for the upcoming wrestling tournament, Gerry promises to bring home two trophies...
Gerry hatches a new "get rich quick" scheme selling counterfeit One Direction merchandise when he finds out the band is in town. But making countless beaded bracelets at home is tedious work, and Gerry soon realizes he has a whole classroom full of potential unpaid labourers just waiting to be exploited.
When Gerry is suddenly promoted from sub to full-time teacher, his initial thrill is quickly squashed by the realization that he’s back to real teaching responsibilities.
When Gerry learns that former Olympic champion Donovan Bailey is coming to town, he's determined to seek retribution for a long-standing bone he has with the track “star.”
Gerry and Simon are both assigned student teachers. Gerry is thrilled to have a minion picking up the slack, while Simon is anxious about the added responsibility. Gerry soon learns that his hands-off approach will not work, as his student teacher, Gloria, is terrified of the students and requires Gerry's presence at all times.
After Gerry has an unpleasant run-in with a unionized construction worker, he decides he wants to form a teachers union at Xavier. Meanwhile, Robert reads the riot act when Malik skips out early on his janitorial duties; and Lisa is smitten with Trudy's brother.
Gerry has big weekend plans for a fantasy baseball draft when he's told he has to cover Saturday detention. In an effort to bury the hatchet and come to terms with Lisa's appointment as the new principal, Robert and Lisa have an impromptu heart to heart.
Gerry's been given another coaching assignment, but this time he's helping Ricki prepare for a fencing tournament, and he couldn't be less interested. In an effort to capitalize on Dwyer's recent divorce, Bobbi invites him over for dinner and attempts to seduce him the only way she knows how. Poorly.
When he attempts to reign in a bratty student, Gerry is faced with the wrath of his notoriously overprotective and obnoxious mother. Upon realizing that she has fallen into the role of staff "punching bag," Bobbi attempts to transfer the title onto another staff member. Meanwhile, Ricki sells pencils to Robert and drives a hard bargain.
Gerry accompanies students on a leadership retreat to a nature centre where he meets the beautiful staff member, Jasmine. Lisa finds out that Trudy is running a morbid “death pool” gambling ring. And Simon and Frank’s innocent game of rugby spoons takes an ugly turn.
Gerry is turning forty, and after finding a letter he wrote to himself ten years earlier, he becomes acutely aware of everything he has failed to accomplish. Meanwhile, Simon's ferret goes missing and Lisa wants to impress the chairman of the board of trustees by putting on an elaborate fun fair in his honour, which quickly devolves into a complete disaster.