Larry and Toni, besides being opposed by Collins, are threatened by a hoodlum named Gridley (Grant Withers), who disguises in a skull mask and pirate clothing.

When the disguise fails, Gridley resorts to desperate means to grab Toni's map, including kidnapping, bombing, vehicular homicide, and attempted murder.

[4] An advertisement in the Motion Picture Herald described Hubbard as a "famous action writer, stunt pilot and world adventurer", and stated that he had written an "excitement-jammed yarn with one of the best boxoffice titles in years".

[5] After his work on The Secret of Treasure Island, L. Ron Hubbard also helped with the script for the 1941 Columbia movie serial, The Spider Returns.

The special effects (including the climactic eruption of a volcano and the destruction of the island) were handled by cameraman Kenneth Peach and explosives expert Earle Bunn.

The sinister master of the island was played by veteran serial star Walter Miller; he was a last-minute replacement for Bela Lugosi,[7] who was forced to withdraw after a back injury.