John Cromwell escapes from a gang of "pirates" to Havana, where he meets Kentucky Colonel Hamilton and his daughter Grace. Though threatened by his former captors, Cromwell has a chart showing the whereabouts of a sunken treasure ship, which they set out to find. When he is accosted in his diving gear and the Hamilton party is marooned by pirates headed by Chipman, Cromwell escapes, boards their submarine, and, after the villains are killed in an explosion, rescues the party.—AFI