Dr. Chulock is in a lab working with his team when he gets word that someone important is coming. They all line up and Colonel Lee Wing comes in. Chulock introduces his staff to the colonel and assures him that the virus they have developed is devastatingly lethal. Lee Wing informs Chulock that his request for condemned prisoners as test subjects has been denied and that instead he will conduct his experiments in Japan. They will go as doctors to a conference, giving them a reason to bring in their equipment, and Lee Wing assigns several of his people to Chulock and his team, including a female lab assistant.
In Tokyo, Kelly and Scott are waiting at the airport for their flight back to their States. Kelly is enjoying eggs, pancakes, and syrup over it all. They bump into an agent, Vicki Richards, who pulls them off to the side and asks for a pocketknife. She has the matching half of the blade that Scott produces. Once she's confirmed her identity, Vicki tells them that they've been reassigned to Hokani Island to deal with Dr. Chulock, who is attending a conference there. Their orders are to find out why Chulock is there and she'll be going with them posing as Kelly's wife. They point out that Kelly is a tennis bum and doesn't have a wife and run off to get their luggage.
The agents arrive at the grounds of the hotel and discover they're attending a dietary conference. They sign in and tell the bellboy, Koyo, that they're there to take in the mineral baths. However, they discover that Vicki is already there and has reserved two rooms, one for her and Kelly and the other for Scott. She bustles in and takes Kelly away. Once Koyo leaves, Vicki admits that she's been a spy for eight months and is eager to prove what she can do. She tells them that Chulock is there with two agents and his supposed wife. Vicki has also identified an American doctor, Dr. Bingham from Philadelphia. Kelly sends Vicki to get him a kimono while Scott finds Bingham and stalls him so that Kelly can impersonate him. Once Scott leaves, Vicki produces a bottle of maple syrup for him and Kelly says that she should leave before he starts to like her. She tells him that she'll study her operations manual while she waits for them to return.
Scott finds Bingham's room and realizes that the doctor is black. Figuring that their first plan is blown, Scott says he has an important message for him from Kelly and tells the doctor to wait for it in his room. In the lobby, Chulock sees Kelly sign in as Bingham and asks if he's Bingham. Kelly denies it and explains that he just registered for him. Scott arrives and introduces himself as Bingham, and Kelly goes to Bingham's room. The spy asks Bingham for his help on behalf of the U.S. government.
Chulock explains that every doctor there was invited because they needed to go on a supervised diet. Since Scott is in such good shape, Chulock assumes that he's an infiltrator. He demands the truth and Scott admits that he's a spy. They assume he's joking and demand the truth, but Bingham comes in and explains that he asked Scott to fill in for him because he was reluctant to diet. Chulock accepts his story and goes off with Bingham while Chulock's agents escort Scott out of the room.
Back in their room, Kelly tries to deal with Vicki, who wants to make their husband-and-wife act look convincing. Scott arrives and tells them where they're setting up. Kelly will go in, memorize the labels, and relate them to Scott so he can translate. They go to Chulock's suite and open the door just as the agent posing as Madame Chulock opens the door. The agents claim that they're there for a costume party and barge in, and Madame Chulock tells them to get out. They apologize for going to the wrong room and quickly leave.
Back in the lobby, the agents are waiting when Vicki comes in with Madame Chulock. She explains that she's convinced the woman to let her shampoo her hair and then take photos of her for the woman's magazine she works with. However, Madame Chulock points out that Kelly isn't wearing a wedding ring. He covers but Madame Chulock passes on the offer. Once she leaves, Kelly tells Vicki to stay away from Madame Chulock because she's way out of the novice agent's league. When Vicki wonders what his plan is, Kelly gives her camera to Koyo and has him go into Chulock's room and take photos of everything. The bellboy assumes that he's an industrial spy and agrees in return for a hefty bribe, and Vicki reluctantly congratulates him.
That night, the agents have tea in their room when they hear an ambulance pull up. Kelly goes down and claims that he's doctor, and the driver tells him that Koyo died in the garage when a block fell on his head. When the agent points out that there isn't a mark on him, the attendant admits that Chulock diagnosed the cause of death. Kelly returns to the room and they head into town with Bingham. After bribing the attendant, Bingham examines the body and discovers that someone bashed in his head to cover up the cause of death. The attendant explains that they'll be cremating the body in the morning and goes to answer the phone, and Bingham tells the agents that Koyo died of an accelerated form of the bubonic plague. He takes a smear to be sure. Meanwhile, the attendant tells the caller that Kelly and Scott are there.
Back at the hotel, Bingham tells Scott that they need to get into the lab and obtain a sample of the virus and send it to Washington to come up with an antidote. As Vicki returns, Bingham suggests that he just needs access to a high-power microscope to identity the smear enough to give Washington the information to make an antidote. He admits that there are no guarantees but it's their best chance. When Vicki tries to help, Kelly finally tells her to go to her room, lock the door, and stay out of their way.
As Bingham tries to work out a way to analyze the smear, Vicki returns with the microscope. She explains that she disguised herself as a maid, walked right into Chulock's room, and simply took the microscope. Kelly points out that once Madame Chulock realizes that the microscope is gone, they'll change the virus and make any antidote they develop useless. He tells Vicki to take it back while the agents distract them and gets some flammable alcohol from Bingham.
Kelly and Scott are soon out in the hallway feigning drunkenness. They knock at Chulock's door and Madame Chulock orders them away. The agents refuse and Kelly lights up the alcohol in his glass. It bursts into flames, setting the door on fire. While Madame Chulock and the technicians deal with the flames, Vicki sneaks in through the patio window and returns the microscope.
Back in their room, the agents wait for word from Washington. The front desk calls and informs Kelly that Bingham had a headache but is now better and asks to meet them at the pool. Realizing it's a trap, Kelly and Scott take off and tells Vicki to stay in the room. They go to the pool and three Chinese agents shove them into the pool.
After fighting them off, the agents go back to their room and change clothing. They explain that they were attacked and Vicki reminds them about Bingham. They go to his room and discover that he's dead of the plague. Vicki blames herself and breaks into tears, and Kelly tells her not to let it get to her. Bingham's notes are missing and they start searching the room. Kelly realizes that the virus is in the water pitcher but figures that Bingham must have had at least a few minutes before he collapsed.
A shocked Vicki asks to go to her room to lie down but Kelly tells her to shape up and help. They need a sample of the virus and don't even know if the water pitcher is contaminated. The agents recreate what must have happened and figure that when Bingham realized he was ill, he would have tried to inject himself with something and then call. His bag is empty and the phone lines are cut, so they figure he went into the bathroom. The agents search the bathroom and find the notes hidden in the paper towel dispenser. As they leave, Vicki suggests that they take the contaminated glass and pitcher with them, but Kelly points out if they do, the Chinese will know they're onto them, scrap the virus, and create a new one. They have to get into the lab and get a sample without anyone knowing about it.
Vicki goes to Chulock's room carrying her cases and a camera. She rings the bell and offers to fix Madame Chulock's hair. The enemy agent isn't interested until Vicki says that she just talked to Bingham and he gave her an idea. Flattered, Madame Chulock agrees and invites her in. Meanwhile, Scott and Kelly find the note that Vicki has left them telling them to watch the door while she distracts Madame Chulock.
Once she shampoos Madame Chulock's hair in the bathroom and has her lend down into the sink to rinse, Vicki opens the door and goes back. The agents sneak in, put on masks, and begin searching for samples. Kelly finds the sample tube hidden inside of the barrel of the microscope. Scott takes a sample, being careful to sterilize any traces with a Bunsen burner, and Kelly puts the tube back into the microscope. When they bump a piece of equipment, Madame Chulock glances out but is restrained by the hair dryer. Vicki distracts her by showing her the slip beneath her kimono.
Kelly and Scott get out just in time as Chulock and his agents come back in. Chulock realizes something is up and demands to see her credentials. When Vicki offers to get them, Chulock's agents keep her there and Chulock suggests that she have a drink of water.
The agents hide the sample in their room but realize that Vicki isn't back and go back to rescue her.
Chulock insists that Vicki drink and she tries to avoid doing so. He wonders why she's afraid and figures that she knows about the virus. However, Kelly and Scott storm in and demand to know where Kelly's wife is. Chulock draws a gun on them and ignores the agents attempt to bluff their way out. Seeing it's hopeless, Kelly attacks Chulock and a fight breaks out. With some help from Vicki, the agents subdue their opponents.
Later, the agents get a message confirming that Washington has developed an anti-toxin. Bingham will receive a posthumous Medal of Honor. Kelly lights three chopsticks in honor of Bingham and his sacrifice. Share this article with your friends