The construction of an undersea canal is about to start with the Seaview tasked with placing the first charge, a 50 megaton nuclear bomb. But as it is being lowered an enormous whale swallows it and swims off.

Everyone but Nelson and Crane are removed from the Seaview and replaced by 8 civilians to test new equipment. One of them is a foreign agent who wants to kill everyone on board and use the ship to provoke an incident and start a war..