Slums of Berlin (1925)

A young engineer lies to protect his fiancée, and is later convicted of perjury (after which his fiancée abandons him) and sent to prison. When he gets get, he tries to return to his former life and finds out that's easier said than done--no one wants to hire an ex-con, and when he finds himself broke and homeless, he is "saved" by a local prostitute, and discovers that his only real friends are the people that society deems to be the "lower classes" and "criminals". Just when he is starting to work his way back to "respectability", a situation arises in which he must risk everything he's worked for in order to help out the people who've helped him.