Bill Graw is the leader of the Water Rats, a gang of thieves infesting the waterfront. He is kicked out by the gang when he is ill. He attempts to steal a locket from Elsie, daughter of Dane, a tugboat captain. He is caught, but befriended by Elsie. Bill, restored to health and the chiefship of his gang, saves Elsie from the thugs. Tom Williams, Elsie's sweetheart, is a young police officer. He determines to break up the Water Rats gang. He opens fire, but his fire is returned, and the thieves are about to escape when assistance, brought by Elsie, arrives. The Water Rats seize a motorboat and flee. The police give chase in Dane's tug, with Elsie at the wheel. Bill jumps from the motorboat and swims ashore. Williams follows him, the tug continuing the pursuit of the motorboat. On shore Bill and Williams grapple. Bill is victorious, and is choking Williams to death when the locket which Bill attempted to steal, and which Elsie gave Williams, identifies the officer as Elsie's sweetheart. Bill sees that escape is impossible. He shows his gratitude to Elsie by doing Williams a good turn, and clasps handcuffs on his own wrists. Meanwhile the tug has overtaken and captured the motorboat, and now returns for Williams. Williams, still unconscious when found, is supposed to have handcuffed his man before giving out. Williams is promoted and receives a handsome reward. Captain Dane gets over an original dislike for Williams and the love affair ends happily.