He escapes from Cockatoo Island and under the name of Captain Thunderbolt becomes a bushranger in the New England region, working with his friend and fellow escapee Alan Blake.

Blake has a romantic involvement with a "half-caste" (sic) girl Maggie that equally infringes the norms of the day.

After gunfights with the bushranger at a dance, then at a rocky outcrop, Mannix discovers that he has killed Alan Blake instead.

[10] British censorship requirements meant that the real-life romantic relationship between Thunderbolt and his aboriginal girlfriend Mary, who helped him escape from Cockatoo Island, was not featured in the film when released in Britain.

[3] According to Filmink "Holmes was a bit of a lefty in real life, and he fashions the story so poor old Thunderbolt is a victim of the upper classes.

[3] Captain Thunderbolt was allowed to live at the end of the film because the producers hoped to spin it off into a TV series.