As Donny and Marie perform on stage, their manager, Sid, anxiously waits for the show to end, because they have to catch a flight to Hawaii. At the airport, Charlie, dressed as a priest, occupies a phone booth as Donny waits his turn. Charlie calls his boss, Wong, and informs him he has retrieved the necklace Wong wanted. However, he warns that Webster, who works for Professor Kruse, is also after the necklace. As Donny and Marie wait for the phone, Tricia, a pretty blond approaches. Donny flirts with her but Tricia is not interested. Noticing that Webster is closing in on him, Charlie approaches Marie and gives her the necklace as a gift from his church. Tricia notices the exchange. Moments later, Webster corners Charlie about the necklace, and Charlie swears he doesn’t have it. Donny, Marie, Sid, Webster, Charlie and Tricia board the same flight to Hawaii. During the flight, Webster kills Charlie with a poisoned cup of water. After the plane lands, Wong’s henchmen, Mickey and J.L., find Charlie's corpse. Meanwhile, Webster calls Professor Kruse, saying he suspects that Charlie hid the necklace. When Tricia asks Marie about the necklace, Mickey, J.L. and Webster overhear and see that she's wearing it. Outside, Mickey and J.L. recognize Webster as he follows Donny and Marie. While Mickey and J.L. tail Donny and Marie's limo, Webster steals a car and follows suit. Although Mickey and J.L. force him off the road, Webster manages to jump out and steal a driving school’s car, resuming the chase. Meanwhile, Donny and Marie are oblivious to what is going on around them. Webster forces Mickey and J.L. to crash, but loses control of his own vehicle and flips it. Later, J.L. pretends to deliver flowers to Donny and Marie's hotel in order to get their room number. Tricia shows up in the hotel lounge, and Donny asks Marie to leave so he can be alone with her. However, when Donny asks Tricia out, she suggests that Marie come along. As Donny walks Tricia back to her room, Marie finds her hotel suite trashed, and screams when she runs into Mickey. Rushing to save her, Donny finds Marie fighting off Mickey and jumps in, chasing the intruder outside but losing him in a swarm of fans. Marie speculates that Mickey was after her necklace, but Donny thinks Marie is imagining things. However, Sid tells them he’s hiring extra security. When Wong arrives at the hotel, Mickey and J.L. update their boss on the situation. At the hospital, Kruse and his henchman, Ito, find Webster bandaged from head to toe. Webster can’t talk, so Kruse instructs him to wiggle his toes to answer yes or no questions regarding a picture of Donny and Marie. Ito turns on the television, and as Donny and Marie perform on a local show, Kruse sees Marie wearing the necklace. At the television studio, Sid introduces Donny and Marie to Al, their new security guard. Back onstage, Marie notices Wong staring at her in the audience and becomes flustered. At the hotel, Donny asks Marie what made her forget lyrics during the performance, and Marie reiterates that someone is after her necklace. Donny wants to get rid of the necklace, but Marie refuses and puts it in a jewelry box. Donny leaves the hotel suite, while Kruse and Ito check into the room next door. Moments later, Wong, Mickey and J.L. check into the room on the other side. Alone, Marie hears noises and notices Kruse and Ito peeking through her windows. Meanwhile, someone steals her necklace. In the hotel basement, Kruse sneaks up on Mickey, and Wong sneaks up on Kruse. Ito sneaks up on Wong, and, finally, J.L. sneaks up on Kruse. They accuse each other of having the necklace, but when they realize none of them have it, they assume another party has become involved and form a reluctant alliance. Back in the hotel room, Marie talks to Lt. Alecki, a policeman, about the theft of her necklace. Outside, Donny admits to Sid that he stole the necklace. He feels that Marie is imagining the gangsters and that it is distracting her from her work. Donny throws the necklace into the wishing well, and returns to the hotel room with Sid to find Marie with Lt. Alecki. Alecki tells Donny he found finger prints on the jewelry box and intends to identify the perpetrator. Donny gets nervous and comes up with a plan to have Al, the security guard, secretly return the necklace. Later, Tricia and Marie catch Al breaking in, and Tricia subdues him with surprising ease. Donny returns to convince Marie that it was Al who stole the necklace. Alecki calls and informs Marie there are no strange finger prints on the jewelry box – just hers and Donny’s. Marie realizes that Donny stole the necklace and is furious. Meanwhile, Kruse hears from his contact at the police lab about the fingerprints. Wong speculates that this was a clever ruse by Donny and Marie to throw him off the trail. The next day Alecki suggests Marie take the necklace to a local museum and have it appraised. Unbeknownst to Marie, the expert she’s meeting is Kruse. Kruse tells Marie the necklace is worthless and tries to convince her to give it to him, but she decides to keep it just as Donny shows up, and they leave the museum on a motorbike. Kruse, Wong and their henchmen give chase, and Donny recognizes Mickey as the guy who broke into their hotel room just as the henchmen start shooting. Donny and Marie narrowly escape, and back at the hotel, they tell Sid what happened. He wants to cancel the show, but they insist they go on. At the show, Alecki brings extra police to keep an eye on the situation. As Donny and Marie perform, they spot Mickey, J.L. and Ito, dressed as policemen, on both sides of the stage. As they flash their guns, Sid notices Ito wearing sandals and realizes he is not a real policeman. Sid notifies Alecki, who arrests Mickey, J.L. and Ito after the show. The next day, Alecki tells Donny and Marie that the three men are not talking, but he confiscated an old map from one of them. Marie notices that the necklace matches part of the map, pointing to a location out in the ocean. Alecki offers to take them out on his boat. At the location, Alecki and Donny SCUBA dive and find a World War II submarine filled with gold bars, retrieving the treasure as Kruse and Wong watch from another boat. Although Kruse and Wong attack, Donny and Alecki fight them off and speed away, accidentally knocking Sid into the water. Kruse and Wong send out a remote controlled jet ski. Unaware that it has been rigged with explosives, Sid climbs onto it. Donny realizes that Sid is in danger just as Tricia arrives in a rescue helicopter. Tricia throws down a ladder and Donny climbs on. They catch up with Sid and pull him off the jet ski just before it runs into Kruse and Wong’s boat and explodes. The next day, Tricia explains that she is with the Navy, and has been looking for the necklace and the submarine for over a year. Donny asks Tricia out on a date, but she informs him that she is married. Donny is depressed until another pretty girl approaches. Donny, Marie and Sid get on a plane to return home.