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The Black Bird is a thief in London's Limehouse district who in another identity is known as his own brother, a crippled keeper of a rescue mission where he is affectionately called "The Bishop." The Black Bird and his rival, West End Bertie, both love the same girl, Fifi, and both promise her a diamond collar owned by a member of London's aristocracy.

A contest of wits between the two crooks results in The Black Bird's shooting a Scotland Yard man and having to retreat quickly behind the disguise of The Bishop.  But this time—so to speak—his joints permanently lock and he cannot resume his original shape; in atonement for his sins, therefore, he decides to give up his underworld life and live as The Bishop.  West End Bertie wins Fifi's love.