Sherlock Holmes Investigates. The Lascar's Fate.

Sherlock Holmes and Dr Watson explore secret tunnels and caverns, which lead them to the workshop of an inventor.
Holmes displays some unexpected knowledge, and his surprising membership in an esoteric club enables him to collect incriminating evidence against a leader of a smuggling gang.
The dastardly Lascar, Ravendra, appears, and a battle to the death allows Watson to show his mettle.