In a hotel in Mexico City, Dr. Rachel Albert enters the lobby and Beltran from the Ministry of Agriculture greets her to the international conference. He helps her check in and explains that Steffanello from Italy and Gerard De Pierrefeu from France have already arrived before her. The next to arrive is Dr. Smithfield from the U.S., and Rachel admits she doesn't know him except by reputation.
The bellboy takes Rachel to the elevator, letting two porters with a trunk get in first. However, the elevator doesn't move and a few seconds later, the porters leave with the trunk... and there's no sign of Rachel.
Scotty arrives in Mexico City posing as Smithfield. The press greets him and Scott is posing as a reporter. Scotty bluffs his way through a brief statement and goes to the restroom where Kelly is waiting for him. Kelly informs his partner that three agronomists have now disappeared into thin air, Rachel being the most recent. They both figure that Scotty will be number four and Kelly assures him that he'll be nearby.
Scotty catches a cab and Kelly follows him in another taxi driven by Hernandez Del Gado. At the hotel, Beltran greets Scotty and the same bellboy takes him to the elevator. Two porters bring a trunk in and they get in the elevator. It stalls and the porters draw a gun on Scotty, chloroform him unconscious, and stuff him in the trunk. Kelly notices that the elevator hasn't moved and that when the porters leave with the trunk, Scotty has vanished. He calls Scotty's room, gets no answer, and realizes what has happened. Outside, the porters load the trunk onto a trunk and leave, and Kelly has Del Gado follow them. The truck heads out on the road but a bus has an accident, cutting off Kelly for a minute. They come to a fork in the road and realize that they've lost the truck.
The truck arrives at a villa outside of town and the men take the trunk inside. They slap Scotty away and the owner, Karafatma, greets him. He introduces himself as Scotty's host and offers him a Turkish bath after his journey. Scotty declines until Karafatma makes it clear he doesn't have a choice. The guards take him to the steam room, give him a massage, and insist that he have tea. When Scotty throws a punch, the guard doesn't even notice.
Kelly checks back at the hotel and discovers that the first clerk, the bellboy, and the porters have all gone on vacation. He admits to Del Gado that he's looking for a man in a trunk and the taxi driver suggests they check out trunk stores. Lacking any other leads, Kelly has Del Gado drive him around and they find a salesman who sold four trunks to the same man.
The guards bring Scotty back to Karafatma, who assures him that he has complete freedom within the walls. Scotty goes out on the patio and finds the three agronomists chatting. Rachel orders Scotty to get them out of there and is disappointed when he doesn't have a plan other than cooperate temporarily with their host. The other agronomists agree with Scotty and an angry Rachel storms off.
Kelly goes to the police station and tries to track who might have been able to move the trunks. When Kelly asks for someone to assist, the officer tells him that he has the perfect man: Lt. Hernandez Del Gado.
That night, Karafatma ushers the agronomists to dinner and their host starts by explaining that he's a freelance spy. Rather than sell information, he sells the source of the information. When Rachel protests, Karafatma points out that arrangements have already been made. Scotty wonders why he didn't pick atomic scientists, their host explains that they don't have enough flair and that each of them are worth $500,000. He doesn't tell them who is buying them but assures them that they will be picked up in two days by boat. Rachel asks what happens if they refuse to work for their new masters and Karafatma says that he doesn't know or care, but warns that they are notably humorless. He advises them to accept the unacceptable but Rachel says she'll never cooperate. She tells Karafatma that Scotty is an imposter, having determined he knows nothing about agronomy.
Karafatma demands to know if Scotty is the real Dr. Rogerfield. When he says that Scotty must be a spy, Rachel is shocked, realizing she may have said too much. Karafatma explains that he must kill him and Scotty points out that he must be a lousy spy because their host isn't thinking ahead. He explains that Karafatma will take damage to his reputation unless he provides four agronomists, and suggests that Rachel was confused. Rachel and Karafatma finally understand what he means and presents Scotty as the real Dr. Smithfield. Karafatma reminds her that he will have to kill all of them if he can't deliver four agronomists, and Rachel plays along, admitting that she as confused.
Kelly and Hernandez seek out villagers in the area that may have seen the same truck pass through four times. They come to a closed section of road and the villagers confirm it has been shut down for a week, and Hernandez and Kelly continue on their way.
At the villa, Scotty approaches Rachel on the patio. She apologizes for giving him away and admits that she thought Scotty was Karafatma's spy, planted to get them to cooperate. He says that he thought she was planted to get them to cooperate, and Rachel admits that she's never asked a man to forgive her. She finally brings herself to do it and tells him that Karafatma showed them the tunnels running beneath the villa. They tried to escape but couldn't find a way out, and Rachel hopes Scotty can find a way. He takes some flowers from a nearby bush and they go to check the tunnels.
Kelly and Hernandez find a dirt road that isn't on the map and drive up it, only to find that it's a dead-end.
Scotty and Rachel explore the tunnels and locate a locked door. The agent breaks it down and finds a tunnel leading to the jetty. However, Karafatma and his guards are waiting for them and take them back with the others. Scotty and Rachel agree that it's not hopeless and Scotty says that he has a friend who could show up. When Rachel asks when he's coming, Scotty assures her that Kelly will be there soon.
The two men end up on the coast and realize they don't have enough time to search. Kelly leaves it up to luck, tosses a stick into the air, and they walk in the direction it points.
Scotty gets an idea and mixes wine and vinegar in a coffeepot. He then pours it into Rachel's empty perfume bottle. Later, Karafatma has the agronomists brought in and offers a farewell toast. Scotty says that he's tired of fighting and Karafatma explains that he's moving on once he delivers them to his employers. The agent suggests that they give the champagne to the three guards as well and pours the drinks, drugging it with the mixture from the perfume bottle.
Kelly finds the jetty and the incoming boat. A man in Turkish robes and a fez is waiting with four trunks and Kelly gets the drop on him... only to discover that it's Scotty. Scotty insists that he can't rescue him and Kelly quickly hides. The boat pulls up and the Asian representative walks over and, assuming Scotty is Karafatma, tells him to open the trunks. The three unconscious guards and Karafatma are inside, and Scotty tells the Asian that they are the four agronomists. Scotty collects the money and the Asian has his men load the trunks onto the boat.
Once the boat is gone, Kelly congratulates his partner. Scotty explains that he created a knockout drug and has a lady to boot.
Later, Scotty and Rachel go back to the cellar and write their initials, now that she knows Scotty's real name. He invites her to draw a heart around it and Rachel admits that she didn't know him. He assures her that she does and they kiss. They then go upstairs while Kelly is preparing the Turkish bath and tells them to get out while he relaxes.