Blackmail (1929)

Alice White, the daughter of a tobacconist, has been dating Frank Webber, a young up and coming detective at Scotland Yard. After successfully ditching Frank one evening on a date, Alice instead meets up with a young male artist who she really wanted to be with that evening. After going up to the artist's studio apartment, he tried to rape her.

She ended up stabbing him to death in self defense, after which, she tried to wipe out any evidence of being in his apartment, followed by sneaking out of the apartment and wandering the streets in a shocked daze over what she did. Frank ends up being one of the detectives assigned to the case, he who sees evidence only known to him of Alice having been in the artist's apartment, and recognizing the dead man as the person with whom Alice snuck off after she ditched him the night before. Frank decides to hide the evidence he knows implicates Alice from his fellow detectives, but confronts Alice with it to see what she says. But before she answers, an unsavory type named Tracy implies that he knows what happened, and blackmails the pair in return for his silence. Eventually, Frank learns that Tracy is a wanted criminal. So Frank comes up with an idea of pinning the murder on him. The questions become whether such a move will actually work, and if so, whether Alice's conscience will allow an innocent man, however unsavory, be charged with a crime he didn't commit.