Sea captain Jim Marsden is about to be hanged for a murder he didn't commit, and is rescued from the gallows by two of his crewmen.

During the search for the killer, one thing leads to another and Jim and the crew soon find that their troubles have just started.

Investigating a possible hiding place of the killer, Jim encounters huge sea monsters in Haunted Harbor.

[2] The serial was re-released on 26 September 1951, under the new title Pirates' Harbor, between the first runs of Government Agents vs. Phantom Legion and Radar Men from the Moon.

[2] Cline writes that this "jungle-horror-mystery-sea-story" includes all of the "cliffhanging tricks Republic could muster.