Phillip Davidson John Mills boards a boat and embraces Fay Driver, Elizabeth Sellars. He then goes below to try to persuade her alcoholic father, Captain Driver, Fred Johnson, not to involve Fay in his criminal activity. However, Boyd John Chandos brings aboard Delaney and two henchmen. When Boyd demands that Delaney pay him £500, rather than £200, a fight erupts, and Boyd knocks Delaney out. A broken oil lamp starts a fire, attracting the attention of the authorities, and Philip is fished out of the water. A charred corpse is found in the sunken boat. The Drivers and Tim Pewsey, John Slater, perjure themselves by identifying the dead man as Boyd, rather than Delaney, and claiming there was no other man present. This leads to Philip's conviction for Boyd's murder. Granted parole, he is released after 12 years in prison.
Upon release, he sets out to get even with the witnesses. He is kept under surveillance by the police on the orders of Superintendent Bob Lowther, who is now married to Fay. Philip finds an abandoned barge claimed by Jackson, a kindly old hermit Michael Martin Harvey. His plan is to live rough on the barge while he searches for the witnesses. But three people attempt – initially unsuccessfully – to befriend him. First, Jackson withdraws an initial request for rent. Then Craig, a newspaperman who suspects him to be innocent, arrives; Philip throws him out, but Craig tumbles down an open hatch and is knocked unconscious, and Philip rescues him Geoffrey Keen. Finally, he happens upon Ilse, a traumatised refugee. When he rescues her and allows her to stay on the barge, she falls in love with him Eva Bergh.
Informed by Craig that Captain Driver has died four years earlier, Philip stalks Pewsey, with Lowther and Craig on his trail. Pewsey is frightened into confessing to Lowther that there was another man present at the murder. Now Lowther's marriage comes under increasing tension as he considers the possibility of his wife's perjury. Finally, she confesses she did lie to protect her father. Lowther tells her that she will have to turn herself in and he will have to resign. She asks for time, and goes to see "George Berry", who turns out to be Boyd. She asks him for money and they plan to leave the country together.
Ilse pleads with Philip to give up his dream of revenge and start a new life with her. He confronts Fay in her home, but realises that Ilse is right, and walks away.
When Fay realises Boyd is not coming, she attempts suicide by trying to jump in front of an oncoming Waterloo & City line train, but is stopped by other people on the platform. She leaves with police sent by her husband after he read her farewell note.
By sheer chance, Philip is then hired to deliver an urgent letter to "Berry". Philip confronts Boyd in his office, initially with a gun, but he throws this aside, deciding to fight like men, but when Boyd picks up the gun Philip runs away. It is time for Boyd to meet Fay at London Waterloo railway station, but he pursues Philip and shoots him in the arm.
Philip flees to the barge, but Boyd is waiting for him. After a chase, Boyd is about to kill Philip when he is shot dead by Jackson.
Ilse and Philip refuse further help from the police. They are left to deal with their pasts and face the future together.
