Scott Walters Dana Andrews is dispatched to London to review a US$2 million policy that names Perry Henderson as the beneficiary, with the policyholder’s elderly mother in mind. Walters hopes to press Perry Henderson for answers, but his first real contact is with Perry’s poised personal secretary, Marian Taylor Jeanne Crain. Walters’s cousin, Arthur Henderson David Farrar, hints that Perry is currently deep-sea diving off the coast of Portuguese East Africa, yet he withholds the crucial detail: Perry’s expedition is tied to deposits of diamonds on the sea bed. Alarmed by the danger, Walters urges Arthur to make Perry pause these risky activities or risk forfeiting the policy.
Walters tries to win Marian’s trust, hoping she might reveal Perry’s whereabouts, but Marian makes it clear she is engaged to Perry. With the plan for a quiet life thwarted, Walters decides to return to America, only to be pulled back when a newspaper headline claims that Perry was swept overboard from the SS Nigeria during a storm off Lourenço Marques. Walters abandons his plane and heads to Marian to relay the grim news, only to discover that Marian’s landlady says she has flown off somewhere. Suspecting South Africa as Marian’s destination, Walters jumps across continents, flying to South Africa to try boarding the SS Nigeria, which has already sailed. He then hops to Beira to catch a ride aboard a coastal tramp, where he shares a compartment with Pitt Wilfrid Hyde-White.
In a storm, Pitt and Walters are the only passengers well enough to join the captain for a meal, and Walters’s habit of probing Perry’s death rattles the ship’s hierarchy. His secretive nature irks the crew, and Walters discovers that the only witnesses to Perry’s death were employees of Perry’s own firm, which also owned the vessel, the SS Nigeria. A secret compartment on the ship yields a cigarette butt bearing Perry’s bespoke marks, and Walters learns that Marian is aboard as well. Marian, when questioned, tells the captain she does not want Walters to trouble her any further.
Another violent storm shifts the tension upward when Pitt borrows Walters’s trench coat to go outside, and a crewman attempts to throw Pitt overboard. Marian’s screams alert everyone, and Walters realizes the assailant mistook Pitt for Walters, aiming at the wrong target. With Marian ashore and the ship’s crew pressing Walters to stay put, he makes a bold jump to follow Marian’s trail, eventually tracking her to Northern Rhodesia. A police superintendent helps Walters locate Perry’s mother, moving the investigation toward the ultimate truth.
Walters continues to chase Marian to uncover Perry’s whereabouts, and the pair grow closer as fascination shifts toward mutual trust. The truth finally surfaces: Perry faked his own death to claim the insurance money. The revelation escalates into a deadly confrontation as Perry tries to kill Walters by giving him a rifle with the firing pin removed so a lion will do the job, a perilous scheme foiled when Vincent Michael Mataka, Perry’s native right-hand man, shoots the lion. Walters and Marian flee together, with Vincent forced to go along, and they are pursued by Perry and his African henchmen. The odyssey spirals through danger—water, gunfire, and the usual array of wild beasts—but a timely police intervention, led by the superintendent, prevents catastrophe. In the climactic struggle, Perry fights Walters and escapes by boat down the rapids, only to capsize; Walters saves him, and Perry is finally arrested. The film closes with soften-edged relief as Walters and Marian embrace, the danger behind them and a fragile peace ahead.
