"The Sea Tiger" is the name of a broken-down bucket of an old freighter, abandoned by the Japanese at the end of WW II, lying in anchor in a New Guiena cove. Co-owners Jenine Duval and Jim Klavier have hired Ben McGrun as its skipper and Joe Edmun as First Mate. Everone has designs on a none-too-secret secret safe which holds a fortune in diamonds, while a another group is after a cache of gold ingots, which the Japanese had hidden and left behind. Klavier is murdered and McGrun is accused and turns investigator to clear himself. The suspects also include Fat Harry the Bartender, and Willaims, a seedy insurance investigator from Sydney, Australia, who may or may not be all that honest.