Calvin finds a decoder ring in his cereal. He tells Hobbes they can now send each other messages in code. He chuckles that Mom and Dad won't be able to understand them at all....not that they do anyway.

Calvin threatens Hobbes some more. Hobbes reminds "Mr. Houdini" he got himself into that mess. Calvin says Mom will kill him for not being at dinner. Hobbes sees the section on Morse code. Calvin says he's sorry and asks Hobbes to untie him. Hobbes tells Calvin how to say "banana" in Morse code. Mom and Dad hear noises upstairs. Dad says it sound like a chair thumping around the room. Mom says his dinner is stone cold. She hopes he's happy.

Calvin tells Hobbes he's going to start a new club, and he can be in it. Calvin explains they'll have secret names, secret codes and secret handshake. They'll have a secret clubhouse with a secret knock. Hobbes asks why all the secrecy? Calvin tells him people pay more attention to you when they think you're up to something.

As they climb down from their tree fort, Calvin says he'll be the strike force commander, while Hobbes is the special agent in charge of munitions. Calvin suggests filling a water balloon and sneaking up on Susie through the back yard. Hobbes wants to be official cartographer, mapping their hiding places and escape routes. Calvin decides to be the code expert and make an unbreakable code. Hobbes runs to get paper. As they both work on their tasks, Calvin says he hopes Susie doesn't go anyplace for a while.

Calvin has finished the secret code. He has assigned each letter a totally random number. For instance, for the letter "A", you write 3,004,572,688. Hobbes admits that's a good code. Calvin says they only have to commit it to memory. He asks if Hobbes has finished the map of their neighborhood. Hobbes isn't quite done yet. He asks how many bricks there are on the front walk.

They have their map, the code, and a water balloon. They're ready to soak Susie. Hobbes says they should run to the big tree out back, then to the bush out front, then the ditch out back, then the tree out front. He explains to a winded Calvin that's to lose anyone who might be tailing them. Calvin is going to write Hobbes a note in code. He asks how to spell "nincompoop".

In their tree fort, Calvin says it doesn't give their club a lot of credit when the First Tiger is a willing captive of the enemy. Hobbes sticks out his tongue. Calvin says they stole her doll, and he had to pay ransom. He says it's a disgrace. Calvin doles out demerits for besmirching the club's reputation and conduct unbecoming an officer. He also gives a censure for not devouring Susie when he had the chance. When Calvin asks if there's anything else, Hobbes tells him he almost gave her their code when she rubbed his tummy. Calvin asks whose side he's on.

Calvin changes his club name to "Hobbes is a Mangy Flea-Ridden Furball". Hobbes declares war on Calvin's club. Hobbes says he'll have maps and secret codes. Calvin says he'll have them too, and his will be better than Hobbes'. Hobbes says he's going to write himself a message in code right now. It will say "Calvin smells like a baboon". Calvin says he's broken the code already, and he does not.

At the dinner table, Calvin asks what the dinner is. Mom tells him to try it. He asks if grubs are in it. Mom tells him to try it. Calvin holds his nose and asks if that means he's going to hate it. Mom yells for him to try it. Calvin says she's mad because he broke her code.

Calvin tells Dad that the meaning of words isn't a fixed thing. Any word can mean anything. He says English can become an exclusionary code. Generations can be divided by the same language. He asks Dad if he thinks that's totally spam. He says it's lubricated, and that he's phasing. Dad gives Calvin the peace sign and tells him marvy, fab, far out.

Calvin isn't sure he wants to open the letter. It might be a mushy poem written with a pink pen in loopy letters. He sees the note is cut and pasted letters from a magazine. Hobbes reads the letter. It contains instructions for a code and says a coded message will follow.

Calvin thinks this is real secret agent stuff. He figures the message must be super top secret and important. He wonders what it will be and when he'll find out. Hobbes says it's a good thing Calvin is the patient type. Calvin is so excited, he has to use the bathroom.

Calvin sits at school with a smile on his face. He thinks it's exciting to get a secret message in the mail. He wonders if the message will arrive in the mail today. Miss Wormwood is trying to tell him something, but he sits with his smile. As Miss Wormwood continues talking to him without Calvin hearing, he wonders who sent it and why was it sent in code. Calvin sits in the principal's office with a smile on his face. He thinks he's growing up to be a spy, since he's so good at figuring out what's going on.

Calvin races inside the house wondering if he got a letter. Calvin opens the coded message. They decode it. It says "Calvin is a porridge brain". Hobbes says some people have secret admirers. Calvin has a secret detractor.

Calvin angrily crumples the coded message. Calvin wonders what kind of depraved maniac would go to so much trouble to insult him. He knows the twisted fiend has too much time on his hands. Mom hands Calvin another letter.

Calvin chases Hobbes. He says Hobbes has been sending the insults. He chases Hobbes around a tree. He stops. He admits the skull drawings were pretty cool. Hobbes says you can tell a good spy by his ominous logo.

Calvin says nothing he does is his fault. He says his family is dysfunctional, so he's not self-actualized. He says his behavior is addictive functioning in a disease process of toxic co-dependency. He need holistic healing before he'll accept responsibility for his actions. Hobbes says one of them needs to stick his head in a bucket of ice water. Calvin says he loves the culture of victimhood.

G.R.O.S.S. makes a plan to write a fake code that "accidentally" will fall into Susie's hands. She'll decode the message saying not to go behind the house, where they'll wait for her with water balloons. Hobbes asks why they just don't hit her with water balloons where she's sitting. Calvin says Hobbes is a good officer, but he doesn't have an executive mind.

Calvin writes a coded message. Calvin writes backwards. He hopes Susie isn't too dumb to figure out the code. Hobbes says cracking codes is second nature to cool spies like them.

The coded message to Hobbes says their plans will be ruined if Susie goes behind the house at noon. Calvin's regret is blowing the best day of his life while he's so young.

Calvin sees Susie still playing. He and Hobbes will walk past Susie and drop the top secret, coded letter for Hobbes. They walk past, drop the note, and Calvin says if it falls into a girl's hands, their plans will be ruined. Behind a tree, Calvin says everything is working perfectly. Hobbes says except she isn't picking up the letter.

Calvin wonders why Susie doesn't pick up the letter. Calvin is frustrated. Hobbes wonders if she wasn't paying attention to them. Calvin thinks it's inconceivable anyone wouldn't be interested in everything they do.

Calvin and Hobbes walk by Susie again. They mention the top secret note again. Calvin mentions Susie finding the letter and spoiling their plans again. Behind the tree, Hobbes sees Susie opening the letter. Calvin was worried he'd have to hit her on the head and read it to her.

Susie reads the coded note. She's suspicious. She yells that she better hurry over to spoil their plans. Calvin says she fell for it, so off they go.

Calvin asks if Hobbes understands the secret plan. He does, but he asks about the secret code. Calvin says the secret plan doesn't need one. Hobbes shows their club charter, which indicates every secret plan needs a secret code. Calvin says the club charter never lies. Hobbes says that's why this is such a great club.

The aliens complain the cold white glop covers them and freezes their innards. Calvin says it's snow. They get it every winter. The aliens complain Calvin didn't tell them about that. He replies that they didn't ask. They say they were overcharged. Calvin tells them "let the buyer beware". The aliens walk off complaining that he's a dishonorable potentate. They demand he bring the planet up to code.