The concept of self-sacrifice is central to this film, as the celebrated investigator "Moto" (played by Peter Lorre) finds himself incarcerated on Devil’s Island. His unusual goal is to befriend convict "Brissac" (Leon Ames), with the intention of aiding his escape back to London. There, Moto hopes to unmask the head of the “League of Assassins,” a group aiming to steal a valuable secret formula from industrialist "Darvak" (Henry Wilcoxon). To maintain his cover, Moto must also evade Scotland Yard, which creates genuine danger as he gets closer to identifying the clever criminal responsible. This is a strong performance for Lorre, who seems entirely at ease in a role that now feels familiar. He receives good support from Ames and Wilcoxon, along with Lester Matthews and Erik Rhodes. Even "Ann" (Mary Maguire), the female lead, has more substance as the story progresses. The film shares similarities with the “Charlie Chan” mysteries; both employ elements of science and logic to facilitate deductions that Moto perceives as obvious to everyone but himself. It's an enjoyable watch.

Source on TMDB