When the gang returns from the Yucatan Peninsula with the ancient spear they think to be the Heart of the Jaguar, they find the town empty! Everyone has been taken underground. Our heroes soon find the townsfolk in chains and digging a vast excavation policed over by Kriegstaffa bots. Professor Pericles and what's left of his Mystery Incorporated are there overseeing the dig. They're looking for the entrance down into the caverns where the cursed treasure and the Evil Entity are buried. Saving all the townsfolk from Pericle's evil clutches, our five young heroes gear up to follow Pericles and his motley crew through the gate and deeper down into the depths.