Phillip Davidson boards a boat and embraces Fay Driver. Then he goes down below to try to convince her alcoholic father, Captain Driver, not to involve Fay in his criminal activity. However, Boyd brings aboard Delaney (a man he has agreed to smuggle out of the country) 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 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. 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. Finally, he happens upon a sailor attempting to rape Ilse, a traumatised refugee. When he rescues her and allows her to stay on the barge, she falls in love with him.

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.

The film was made at Pinewood Studios and on location in the North Kent Marshes on the Thames Estuary, around Gravesend, and at Shad Thames, a street next to Tower Bridge in central London. Many of the houses shown in the film were demolished soon afterwards.^{[citation needed]}

It was the last film of Henry Edwards, a major British star of the 1920s and 1930s, who had a small role as a judge early in the film.

Producer Hugh Stewart said "I thought it was rather good but it didn't do that well."^[5]

The film received its gala premiere at the Leicester Square Theatre on 22 January 1953, with Prince Henry, Duke of Gloucester and Princess Alice, Duchess of Gloucester as guests of honour,^[6] and entered general release the following day.^[1]

The Monthly Film Bulletin wrote: "The story of The Long Memory is one of improbable if ingenious contrivance; one might have expected a fast and fairly exciting melodrama to have been made from it. The director, however, has chosen a slow, slightly portentous and fairly inflexible style with which to frame his events; he has spot-lighted characters and motivations and, by doing so, exposed them. For the truth is that the people are superficially and unconvincingly drawn, and further handicapped by some undistinguished acting. The attempt at a Quai des Brumes (1938) atmosphere barge setting, the outcasts' shack, the love affair of the embittered man and the pathetic refugee – appears strained and unreal. Some good small-part acting (by Vida Hope, Thora Hird, Geoffrey Keen and Harold Lang) and the excellent location work in and around Gravesend are not enough to disguise a confected intrigue among wooden characters. There are obviously intelligent talents at work, but they are misapplied."^[7]

The Radio Times Guide to Films gave the film 2/5 stars, writing: "Robert Hamer will always be remembered as the director of the classic Ealing comedy Kind Hearts and Coronets (1949), but he also had an excellent eye for local detail. Here he cleverly captures the murky side of life in London's marshlands, but he is beaten from the start by the utterly predictable wrong man story. John Mills is badly miscast as an old lag desperate to discover who framed him for murder, while detective John McCallum is clueless."^[8]

The Times film reviewer found the film a bit dull and self-important, but gave director Hamer credit for "effective use of the film's natural background, the mud and desolation of the flats of the Thames Estuary."^[9]

• The Long Memory at IMDb  
• The Long Memory at the British Film Institute^{[better source needed]}
• The Long Memory at BritMovie (archived)
• The Long Memory at Ferdy on Films
• Britmovie: Film locations
• The Long Memory then-and-now location photographs at ReelStreets