While investigating panic among the Monkey People, Zandor confronts a giant spider and is bitten and poisoned. Dorno must go to the six-legged mustachioed Spider People within the Endless Caves with the Herculoids to get the only known antidote. The Spider People capture Dorno to hold him hostage. The Herculoids eventually stage a rescue, get the antidote, and block the Spider People's caves to cover their escape.