The oceans are leaking through a fissure in the ocean floor. A con-man named Muldoon agrees to guide Mark through the fissure to investigate. However, Mark is unaware either that giants inhabit the other side of the fissure or that Muldoon has already stolen gold from one of them.

Mark re-encounters Muldoon, his nemesis from "Giant," who is using a sea monster to make island natives sacrifice young girls to him.