In 1971, British photographer Richard Bryant dives into a mountain lake, the "Finstersee", and retrieves a box. Two local men later confront him, demanding to know where he has put the chest. When Bryant refuses to answer, the younger man strikes him, causing Bryant to fall and strike his head on a rock.

US lawyer William "Bill" Mathison is on holiday in Europe and visits Bryant's photo shop in Salzburg to ask about a book of photographs of Austrian mountain lakes. He is acting on behalf of publisher James Newhart. Bryant's wife Anna hands Bill correspondence from Eric Yates, Newhart's representative in Zurich, including a countersigned cheque for the illustrated book.

During the visit, Anna's brother Johann Kronsteiner receives a call from family friend Felix Zauner, who says that Bryant was the victim of a fatal accident. Johann goes to identify the body at an inn close to the Finstersee. The inn's landlord, Grell, is the elder of the men who had earlier confronted Bryant.

Outside of the photo shop, Mathison notices that he is being followed by two men. To lose them, he takes a hackney carriage and is driven through the city. Having shaken off the first tail, a heavy set man also starts following him. Bill takes part in a tour of Hohensalzburg Fortress, and eventually loses the man.

While admiring the view from the fortress, Bill meets the young American Elissa Lang. Mathison eventually invites her for a drink at his Salzburg hotel. She actually works for Zauner, who is part of the Austrian secret service. However, she is also working for the Russians as a double agent and passes information to KGB agent Lev Benedescu.

While Johann drives to the Finstersee, Bill receives a visit from Anna, who talks about her husband's death. Anna is convinced that her husband has been murdered. She asks Bill whether Yates is involved in this affair, but he explains that Yates is also dead.

Both Anna's husband and Yates had once worked for the British secret service, but she never trusted Yates. She believes that her husband may have once again got involved in espionage. While Bill is taking Anna home, Elissa breaks into Bryant's shop and steals the photos taken at Finstersee, as well as his correspondence with Yates. Arriving at the shop, Bill and Anna discover that someone is inside. Elissa flees unrecognised, but is pursued by Bill. In a side alley, Elissa is confronted by a stranger, whom she overpowers and kills. Bill and Anna find the dead man, who Anna recognises as Bernard Dietrich, Zauner's deputy.

At Finstersee, Johann is looking for the missing chest and is followed by two neo-Nazis, one of whom is Anton – Bryant's killer. Johann discovers the chest at the edge of the forest and escapes from the neo-Nazis. Then, he hides the box at the home of his girlfriend Trudi Seidl.

Bill takes the distraught Anna to his hotel and rents a room for her there, because she would probably no longer be safe at home in the shop. Her brother Johann visits her the following morning. Johann says that he has found and secured the box and reports that an Israeli had come to see him and offered to buy Bryant's chest. Obviously, its contents must be valuable.

Anna reminds Johann that Bryant and Dietrich died because of that chest and that it would be better to give it to Grell, or destroy it. Meanwhile, Bill meets up with CIA agent Chuck, who has contacted him through Newhart. En route to their meeting, Mathison is again followed the moustachioed man, who Chuck arranges to be shot by an assassin. According to Chuck, the dead man had been a Polish spy working for the Chinese. The CIA had been working with Yates, who had been another double agent. The chest contains documents listing former Nazis who are still active, and who have infiltrated the West or are being used by Western intelligence services. The Russians have recently discovered a similar chest in Czechoslovakia, and have the lists already. Germans named in these lists are working in important scientific positions for the USA and are now vulnerable to blackmail by the Soviets, so it is vital that the CIA knows their identities.

Johann returns home, where the two neo-Nazis are waiting for him. They kidnap him. At the photo shop, Anna receives a call from Trudi, who says that Johann has not kept a date with her.

Bill drives Anna to her husband's funeral and waits at the entrance to the cemetery. Two men grab Anna and drag her into a car. Bill notices and follows the car towards the city. He gets in front of the kidnapper's vehicle, slowing it down and causing enough traffic chaos to ensure that the Austrian police become involved. Anna is rescued and the men are arrested. Meanwhile, the neo-Nazis begin torturing Johann. They want to know where he hid the chest. Elissa meets with Benedescu, who is annoyed that she has failed to get rid of Bill. Benedescu hands Elissa a bomb with a 10-minute timer. After verifying that the chest is genuine, she is to use it to destroy the box. The Russians do not want anyone else to access the lists.

Worried about Johann, Anna and Bill want to meet Trudi, but see Zauner's vehicle on the road. They find him in his shop and he reveals how to find Trudi. Then Elissa appears on the scene. Sensing danger, Bill takes Anna out of the shop. Zauner knows that Elissa is responsible for Dietrich' death and says that the Austrian secret service knows about her double agent activity. Elissa assures Zauner that she only wants to destroy the chest, which seems to suit him. Elissa goes to the inn and meets a group of neo-Nazis, led by Grell, and announces that she is desperate to get her hands on Johann in order to learn the chest's location. Grell then calls Johann's kidnapper Anton.

Elissa pretends to be Anna on the phone and tries to convince Johann, who is already worn down, to hand over the chest, otherwise Trudi's life will be in danger. Johann passes on the box's location, but also reveals where he is being held.

Meanwhile, Chuck shows up in Bill's car and all three go to see Trudi. Trudi hands over the chest. They are about to leave when Elissa and the Neo-Nazis arrive, followed by Felix Zauner. Zauner and Mathison interrogate Grell, whose henchmen have disappeared, while Elissa attaches her bomb to the chest. The explosion comes sooner than expected (as planned by Benedescu) and kills Elissa.

Chuck takes Grell into custody and Zauner tells Bill that he knows where Johann is being held. On the way there, Bill confesses that he and Chuck had swapped the chest for a duplicate. Zauner, in turn, reveals why he was so interested in getting the chest: his name is on one of the lists. He had once served as a Nazi informant to save his wife from deportation to a concentration camp during World War II, and the KGB had been blackmailing him. This was why he agreed to help Elissa.

Arriving at the hiding place, Zauner tries to negotiate a deal to take Johann without bloodshed, but Anton kills him. At gunpoint, Bill disarms the neo-Nazis and rescues Johann. Bill and Anna later leave Salzburg together, driving Zauner's Porsche.

• Barry Newman as Bill Mathison
• Anna Karina as Anna Bryant
• Klaus Maria Brandauer as Johann Kronsteiner
• Karen Jensen as Elissa Lang
• Joe Maross as Chuck
• Wolfgang Preiss as Felix Zauner
• Helmut Schmid as Grell
• Udo Kier as Anton
• Mischa Hausserman as Lev Benedescu
• Whit Bissell as Newhart
• Raoul Retzer as Large Man
• Elisabeth Felchner as Trudi Seidl
• Bert Fortell as Rugged Man
• Adolf Beinl as Anton's Companion
• Patrick Jordan as Richard Bryant
• Eduard Linkers as Tour Guide
• Christine Buchegger as Waitress
• Johannes Buzalski as Telephone Technician

Roger Greenspun of The New York Times wrote "With twice too many characters and three times too much plot, the Oscar Millard screenplay of 'The Salzburg Connection' might have defeated the best of directors. Against Lee H. Katzin ('Le Mans,' 'Heaven With a Gun') it isn't even a contest."^[3] Arthur D. Murphy of Variety described the film as "erratically limp" as "[t]he action plods through some beautiful scenery," adding, "The score sounds like a mish-mash of badly-selected transcription library stock themes."^[4] Gene Siskel of the Chicago Tribune gave the film half of one star out of four, calling it "a lethargic and completely confusing spy story" that amounted to little more than "90 minutes of 'box, box, what's in the box?' This, of course, isn't revealed until the final minutes, at which point there is nothing that could be in the box which would save the movie."^[5] Charles Champlin of the Los Angeles Times called it "the worst motion picture I've seen all year...The least comprehensible, the least involving, the least interesting, the least entertaining, the least well-conceived, the least successful at bringing off what it set out to bring off."^[6] Gary Arnold of The Washington Post declared it "one of the least exciting espionage thrillers I've ever laid eyes on," adding "As the movie wends its unsuspenseful, uncharismatic, confusing-to-boring way, you hear the audience squirm and feel its spirits sag."^[7] Clyde Jeavons of The Monthly Film Bulletin wrote "Full advantage is taken of the picturesque Salzburg locations...But nothing can redeem the indecipherable storyline and ham-handed direction (which includes gross misuse of slow-motion and freeze); and even the most indulgent aficionado of the spy genre will find this example hard to take."^[8]

• The Salzburg Connection at IMDb  
• The Salzburg Connection at AllMovie
• The Salzburg Connection at the TCM Movie Database
• The Salzburg Connection at the American Film Institute Catalog