'Godzilla: King of Monsters' volgt de heldhaftige pogingen van het crypto-zoölogische agentschap, Monarch genaamd, dat het opneemt tegen een reeks reusachtige monsters. Onder hen bevinden zich de machtige Godzilla, Mothra, Rodan en de aartsvijand, de driekoppige King Godirah.

A 17th-century Caribbean port rumored to have frequented by pirates rises from the ocean floor, where it came to rest after an earthquake many years before. A scientist wants to study it, some thugs want the treasure alleged to be stored there, a bunch of mutated giant crabs living there attack them all.