Lincoln and Clyde are playing secret agents, having been inspired by a new series of comics they've been reading called David Steele. After a failed attempt at stealing a color-changing spoon from Lola, Lynn barges in the house to announce that they have new next door neighbors. The family quickly go over to greet their new neighbors, Jeff, Carly and Ryan Miller, where they suspiciously decline a cherry pie Lynn Sr. made for them.
Later that night, while Lincoln brushes his teeth, he notices some bright lights shining through the window. Pulling out some binoculars, he discovers the Millers working a giant machine in their attic and Ryan suspiciously closing the blinds. Lincoln quickly tells his family that the Millers are actually spies, but the family refuses to believe him, as he has a habit of being suspicious about new neighbors. Lincoln leaves and calls up Clyde, who is revealed to already be at the Loud House and correctly predicts what's on Lincoln's mind. Now that they're together, the two proceed to gather any suspicious evidence.
The next day, Lincoln and Clyde proceed to go around town, spying on the Millers. During their investigations, they spot Jeff going to the library, where he meets up with a woman in a trench coat and obtains a book on how to grow Georgia peaches. While spying on Carly at Flip's Food and Fuel, the boys discover her purchasing a peach flavored Flippee, and when Flip asks if she wants the highly preferred cherry flavor, she audibly voices her disgust for cherries. At the middle school, Lincoln and Clyde drop a secret microphone on Ryan's slice of pizza and eavesdrop on a conversation between him and Lynn, where he says he'll be busy doing other things, where his statement of taking out the trash causes Lincoln to remark that it's not garbage day today. With their first pieces of information obtained, Lincoln and Clyde proceed to get to work on what they could be planning. Reading more David Steele comics and gathering more evidence, Lincoln comes up a conclusion: he suspects that the Millers are part of a secret organization called S.U.S.P.E.N.S.E. (Secret Underground Society of Peach Entrepreneurs Nixing Sour Exports), and their plot is to destroy all the cherries in Royal Woods, which, according to Clyde, would cause their economy to collapse as cherries are the main export of Royal Woods. When Clyde questions how they can stop them, Lincoln says that he knows the perfect distraction.
Later, a barbecue is held at the Loud House, as Lincoln wants the Millers to feel welcome. With the two families distracted, Lincoln has Charles open the door of the Miller's house and enters. After Lincoln affirms that he's inside, Clyde, on lookout duty, is discovered by Lola, who tattles to everyone via megaphone that Lincoln is sneaking in the Miller's house. With everyone warned, the two families quickly rush over the Miller's house, and just as Lincoln spots the machine and attempts to shut it down, he is caught by the two families. Lincoln tries to explain that the Millers are actually spies and the machine he found is a device that's going to destroy all the cherries in Royal Woods. The Millers laugh, saying that the machine is actually a console that predicts the weather, since they work for the weather service. Realizing he was wrong, Lincoln apologizes, and the Louds leave, ready to punish Lincoln for causing trouble. When Clyde calls up Lincoln to ask if the mission was a success, Lincoln declines and declares the mission a failure. When Lincoln tosses his walkie-talkie, he unknowingly hits a button on the weather console that reveals a secret room with a machine ready to destroy all the cherries in 20 seconds. As the Louds react in horror that the Millers are actually spies working for S.U.S.P.E.N.S.E. (meaning that Lincoln and Clyde were actually correct this whole time), Lincoln manages to evade them and successfully aborts the machine from destroying all the cherries. When the Millers proclaim that they won't stop until they make Georgia peaches the top fruit in the world, the Louds are about to report them to the FBI, but the Millers use a peach-shaped smoke bomb to disappear and evade capture.
That night, the Louds watch the news, where Katherine Mulligan states that authorities are on the lookout for the Millers and congratulates Lincoln and Clyde for foiling their plans on destroying all the cherries. Rita apologizes for not believing in him and Lincoln says that he got carried away. At that moment, Lynn enters and says that some new neighbors have arrived. Just as the family is about to leave to greet them, Rita stops them, saying that they made a deal: Lincoln has to spy on them first before they go meet them. Donning his spy suit, Lincoln calls up Clyde and leaves, ready to investigate their new neighbors.