Maurice, known by the codename of Numbuh 9, was a member of Sector V and was said to be one of the best operatives in the Kids Next Door. Three years ago, he vowed to find the source of the teen's chicken pox was hit with the Pox and injured Sadly, though he was able to find his target, he turned 13 before he could destroy it and was decommissioned before he could complete his mission. He was so well-loved by his teammates that even Numbuh 86 was reluctant to decommission him, and everyone cried when his memory was wiped, turning him into a typically mean-spirited and snobbish teen.
After Maurice was decommissioned, the current members of Sector V, especially Numbuh 5, who had known and looked up to him when she was young began monitoring him to ensure that he was not recruited by the Teen Ninjas and turned into an enemy, even though it was against KND regulations for them to interfere with a decommissioned operative's life. However, Maurice soon got into a relationship with Cree, who took him to Chickenpox Island to assist her and the other evil teens in their new plan to use the recently built Chickenpox Cannon on a children's street fair with Chickenpox during their high school football rave. After being infected with Chickenpox by Cree, Numbuh 5 went alone to save Maurice.
There, Maurice reveals that he was never actually decommissioned in the first place, and had become a secret undercover Teen Operative who was allowed to secretly stay in the KND after turning 13, a position only reserved for the KND's best operatives. He defeated Cree, poxed the McClintock High School students and destroyed Chickenpox Island, all without the Teen Ninjas finding out his secret. Before returning to his undercover life, Maurice implied Numbuh 5 might be selected to remain in the KND as an undercover operative after turning thirteen.
He was later seen in Operation: V.I.R.U.S. at the high school prom with Cree.
He later appeared with a speaking role in Operation: P.A.R.T.Y., attending a party at the Delightful Mansion From Down The Lane with Cree while Father was away. When the Delightful Children begged Sector V to get all the troublesome teenagers out of their home, he was dragged off to the basement by Cree to find Father's secret sanctum, with Numbuh 2 and Numbuh 5 following them.
Maurice discovered Abigail and pinned her to the wall, and asked her what she was doing at the party, to which she asked Maurice what he was doing with her sister. They got into a small fight as Maurice explained that he was on a mission as an undercover operative to figure out what Cree's plans were.
It turns out that Cree wasn't up to anything villainous at the party and only wanted to be alone with Maurice to make out with him, but the moment is ruined when he tells Cree that she smells bad (because the KND stole her deodorant). Then Numbuh 5 jumps out in front of them and makes fun of her sister's smell until another teen appears to warn them that Father is returning home. Maurice made no further appearances in the episode (or the series, for that matter), but was presumably (due to his cunning) evacuated from the mansion before it exploded.