Ben, Gwen, and Kevin are summoned to the Plumbers’ Academy to complete their basic training for Plumber duty, as they originally received their deputy Plumber titles on the field. At the academy, they befriend an alien named Tack, while Ben comes at odds with their instructor, a strict yet decorated Plumber named Magister Hulka. As they train, several incidents occur which lead Ben and the team to suspect that someone is targeting Hulka with the intent to assassinate him. Investigating, they eventually discover that the attacker is Kolar, a Tetramand and one of Hulka’s old foes. Together, they defeat Kolar and send him to the Null Void. Ben, Gwen, Kevin, and Tack then graduate from the Plumbers’ Academy and are made formal Plumbers, while Hulka gives Ben an award for his creative tactics.