Tenement dweller Molly Moore, trying to forget her crooked past and go straight, runs a cheap restaurant in the underworld district in order to educate her younger sister Marion.
Peter James Slaney, just released from prison, is the only boarder who is kind to Lena, the maid at the cheap Paris Hotel. So that Lena can leave her abusive landlady, Slaney accepts $2,500 from a stranger, who threatens to send Slaney back to prison unless he undertakes a job. Slaney is sent to the home of political boss John Biggs with a sealed envelope which he is to open after entering.
At 10 years old, Owen becomes a ragged orphan when his mother dies. Abusive next-door neighbors the Conways take him in, and by 17, Owen has learned that might is right. At 25, he's a career gangster: loitering, gambling and drinking in dens of iniquity. Marie Deering arrives in Owen's area, eager to empower the impoverished, gang-affiliated youth through education. Owen slowly but surely leaves his old life behind, choosing the narrow path- all the while falling in love with Marie. Skinny, who's taken over Owen's role in the gang, reappears to him, spelling trouble.
After being falsely accused of theft, Pete, the station master's assistant, rescues his girlfriend from the genuine villain, marauding crook Desperate Dan.
A man falls in love with a piano player and tries to woo her. A passerby hears a maid's music, fancies he's found his true love, and chats her up. Her boyfriend arrives for his music lesson and jealously dismisses the interloper, who swipes a grinder's organ (and monkey) to help him serenade the maid. Later he follows the boyfriend to a residence hotel and plants a bomb in the man's piano. The organ-grinder is gunning for the thief, and soon the piano, bomb, monkey, thief, and pistol-packing grinder are rolling down the road to the delight of maid and lover. It's ka-boom for some and a kiss for others.
