The Grand Mistress

The Grand Mistress was an antagonist in S03E02 'Spy For A Day'. After Avril Franklin, Scoop Doggy and Davina Berry volunteered for the Be An M.I.9 Spy For A Day program, they are tasked with stopping the shipment of nuclear warheads. The Grand Mistress, of self-declared criminal organization SKUL, was revealed to be the mastermind behind this, and the trio have to stop her before she initiates her plan.

However, she attempts to capture the three and lock them in a cage as they appeared too inept to fight a group of SKUL agents. Avril begins developing a burning hatred for the Grand Mistress, commenting on her smug demeanor.

The attempt to lock them in a cage further enrages Avril. She eventually snaps; decapitating her and mutilating her body in front of SKUL's "leader": The Grand Master himself. Thanks to Avril's mental snap, the three new spies save the day.

Her tombstone at the end of the episode reveals she was born on March 17, 1949, and died on January 10, 1999. It was revealed that she was the mentally tortured lesbian daughter of a wife of the Grand Masters' father.

Avril later boasts her murder throughout the rest of the series, going as far as to add it on her resume in Season 5.