They Came From The Gateway (Part 1 of 2) Martin Mystery : Season 2 Episode 13

When M.O.M. ceases to return from her Jamaican vacation, Billy calls in Martin, Diana & 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! Halloween theme music)