When M.O.M. fails to return from her vacation in Tibet, Billy calls in Martin, Diana, and Java to investigate (despite the fact that Martin has been temporarily suspended from the Center). They uncover what M.O.M. was really up to — she was on a secret mission to unlock the Gateway to the Underworld!
General Tropes:
- Achievements in Ignorance: Diana is convinced this is the only way Martin could have gotten a 901 in his college application test.
- Animalistic Abomination: The Underworld creatures are vaguely animalistic monsters that apparently can't be stopped.
- Brainwashed and Crazy: M.O.M. is taken over by the power of the Underworld, intending to use all the creatures trapped within it to destroy the world.
- Humanoid Abomination: The Gatekeeper. He's a floating, vaguely human-looking being in a black cloak with glowing red eyes.
- Never My Fault: Martin refuses to accept his mistake and apologize to M.O.M. for damaging his office even more so than usual.
- Riddle Me This: The only way for Martin and company to enter the Underworld, they have to answer the Gatekeeper's riddle correctly. Martin answers correctly.
