In Acapulco, Mexico, local resident and wealthy American businessman, Walter Thoren, is mysteriously killed in a car wreck. Several weeks later, the board of directors at a New York-based insurance company meets to discuss Thoren’s policy. Since the police and coroner confirmed the death as accidental, the insurance company is obligated to pay a $5 million claim to Thoren’s widow. Before proceeding, however, company executive, Mark Elmes, insists on hiring renegade investigator, Jake Dekker, to explore the possibility of insurance fraud. In preparation to work undercover in Acapulco, Jake calls a modeling agency about employing a woman to pose as his wife, and the secretary assigns him the beautiful Ellie Morgan. Upon arrival in Mexico, Jake pretends to be a successful writer, and he and Ellie rent a luxurious villa next door to the Thoren family residence. That evening, the duo is invited to a party at the neighboring home of Fons Ortega, who was Thoren’s best friend and attorney. Dressed in a sexy gown, Ellie makes an impression, especially with Karl, Thoren’s son, who is well known in Acapulco as a playboy. During the party, Jake and Ellie are also introduced to Joanna, Thoren’s daughter. The following day, Jake convinces a reluctant Ellie to help plant surveillance devices at the Thoren residence. While lounging by the swimming pool with Karl and Joanna, she finds an opportunity to rig the telephone inside the house. During the visit, Joanna mentions a letter her father wrote on his sailboat before he died, but Karl interrupts the conversation before Ellie can learn more. Meanwhile, in town, Jake meets with acquaintance Al Marcus, a veteran investigator residing in Acapulco, and hires him for the case. Through an informant at the local bank, Al has already discovered that Thoren was withdrawing large amounts of money for the last two years and even sold businesses to maintain his cash flow. Jake speculates that Thoren was being blackmailed. Back at the house, Ellie updates Jake on her progress with the surveillance and mentions the letter. While Jake is impressed with Ellie’s detective skills, he is also attracted to her, but resists mixing business and romance. That evening, Jake sneaks into the Ortega house and finds documents proving that Thoren was being blackmailed. Since the fatal accident, Mrs. Thoren has become the target of extortion. Jake tells Ellie that he is on the verge of solving the case and proving Thoren’s policy invalid, which means the insurance company will pay him a percentage of the claim, amounting to $500,000. The following day, Al informs Jake that Ortega and Thoren frequented the Villa del Mar sauna, which was recently purchased by the mafia. According to Al’s source, Ortega and Thoren stopped visiting after their regular masseur was replaced by a man named Dobbs. While Jake leaves to investigate the sauna, Ellie decides to take a SCUBA diving lesson. As the instructor leads the group on a dive, she swims to the Thoren sailboat to search for the letter Joanna mentioned. While underwater, she is attacked by a thug named Kunz from the local mafia, and almost drowns until the SCUBA instructor rescues her. After the incident, Al warns Jake that the undercover operation has been exposed and suggests Ellie fly home. That evening, Jake treats Ellie to a romantic dinner and buys her a large teddy bear. Elsewhere, Al visits Dobbs’ home and finds the masseur murdered in the bathtub. In the living room, he stumbles upon newspaper clippings revealing that Thoren was a former Nazi undercover agent whose real name was Heinrich Stressman. After Stressman was caught spying in the U.S. and jailed, he murdered a prison guard named Dobbs in Florida and escaped to Mexico, where he created a new life. When Al shares the information with Ellie and Jake, the trio surmises that the masseur, Dobbs, was somehow related to the guard. After discovering Thoren’s true identity, he must have alerted the mafia at Villa del Mar, who began blackmailing the German. Meanwhile, at the Thoren home, Frank Gela, the local mafia chief in Acapulco, threatens Mrs. Thoren with additional extortion. She, however, warns Gela that her husband wrote a suicide note in which he named Gela and his associates as the blackmailers. Gela advises her to burn the letter and leaves. Later that night, Jake arrives at the Thoren house and discloses to the family that he is an insurance investigator; however, Karl says he was not fooled by Jake’s cover. Jake encourages the Thorens to trust him and hand over the suicide letter, while reminding them that the blackmailers are ruthless killers. The family, however, is unwilling to cooperate, and Jake leaves. Back at the villa, Jake and Ellie take shelter and survive a shotgun assault from Gela’s hooligans. Afterward, Jake apologizes to Ellie for putting her life in danger and insists she return home tomorrow. The couple kisses and spends the night together. After a tearful goodbye in the morning, Ellie drives to the airport, accompanied by Al. On the way, Gela’s men ambush them, and a chase through the streets of Acapulco ensues, until Ellie’s car is eventually cornered. The hooligans knock Al to the ground and kidnap Ellie. Meanwhile, Karl arrives at the villa looking for Jake. To keep Gela from finding his father’s suicide note, Karl hides the document in the head of Ellie’s teddy bear, which was torn apart by bullets during the gunshot assault. Later, Karl arranges to meet Jake at a church, but he is murdered by Gela’s men before Jake arrives. Returning to the villa, Jake receives a telephone call from Gela instructing him to deliver the Thoren letter and the Ortega documents in exchange for Ellie’s release. Instead, Jake and Al plan to infiltrate the warehouse hideout where Gela is keeping Ellie. Parasailing to the location, they access the building through the roof, but the hooligans hear the intrusion and attempt to shoot the investigators. As Jake and Al fend off the attack, they pounce on Gela and rescue Ellie. Later, at the villa, Jake, Ellie, and Al meet Crawford, a representative of the insurance company, who informs Jake that the firm is under no obligation to pay him the percentage of the claim, since Jake did not prove that the claim was invalid. When Al accidently knocks the teddy bear’s head, the hidden suicide letter surfaces, providing the necessary evidence to void Thoren’s policy. After Jake tells Crawford that the insurance company owes him $500,000, he, Ellie and Al celebrate their newfound wealth.