After Danny Dolan, a police officer newly assigned to the harbor precinct, rescues a drunk who has fallen into the water at New York's Pier 13, Danny is promoted to detective. The detective who was with Danny at the time, Al, is reprimanded because after he fell into the water as Danny was rescuing the drunk, some mobsters whom Al was sent to watch got away. Duke Castenega, the leader of the gang, visits his ex-lover, Kate Riley, at the bank where she works, and although she is about to be married, she realizes that she still loves Duke, who plans to get a list of combination numbers for safe deposit boxes from her. Kate's sister Helen, who works at a chowder house by the pier, has enjoyed bantering with Danny since he began his beat. After Kate marries Eddie Collins, and Duke is arrested, Duke's brother Baby Face visits Kate and urges her to give him the list of numbers. Danny and Al come to the wedding party because of complaints of noise, and Danny is greatly relieved to learn that it was Helen's sister, and not Helen, who got married. Duke is sent to prison, and when Eddie has to go to Cuba, Baby Face tries to force Kate to give him the numbers, but she refuses. During a date with Helen, Danny turns out the lights and tries to kiss her, but she slaps him and he leaves in a huff. Later, Danny apologizes to Helen, and he confesses that things are hard for men: if they don't try to neck, he says, women will think they are too slow; while if they do, they think they are fresh. She says it is the same for a woman: if she lets a guy "maul" her, he will think she's no good; while if she doesn't, he will think she's old-fashioned. They realize that they have fallen in love and kiss. After Duke escapes from prison, Danny's captain offers a promotion, and the newspapers offer a $10,000 reward for Duke's capture. Duke hides in Kate's attic, and Eddie's father Sarge, a paralytic who can only blink to communicate, sees them together. After Helen agrees to marry Danny, Sarge tries to communicate that Duke is in the attic. Danny and Helen plan to get a Morse code book the next day to see what he is trying to tell them. Duke and his gang invade the home of a family living just above a bank, and after drilling through their floor, and using a blow torch to blast through the bars, iron vault and safe deposit boxes, they escape with $87,000. Meanwhile, Helen deciphers Sarge's message and runs to Kate's home. Danny finds a carbon of the message and follows. After Helen orders Duke to leave, Danny arrives. She pleads with him not to arrest Duke in the house to protect her sister, but he angrily refuses, upset that she wasn't "square" with him. Duke hides in the attic, but Danny breaks through the skylight and shoots him as he tries to escape. Danny then tells his captain that he chased Duke from Pier 13, and that Duke broke into Kate's apartment. Kate cries as she thanks Duke, and he warns her to stick to Eddie. After Helen and Danny marry, they escape the celebration and head to the pier, where they plan to leave for Bermuda. Eddie, Kate, Pop Riley and Sarge follow, however. Danny, who shares the reward money with Sarge, tells him it is nice that he did not tip off Eddie about Kate.