Gumball and Darwin somehow get locked in the bathroom together. Believing they will die soon, Gumball tells Darwin a secret he has been keeping for a while - he was the one who had drawn a creepy picture in Darwin's schoolbook, causing Darwin to receive a counseling session over the summer. After a moment of anger, Darwin starts to tell Gumball of a secret that he has been keeping. Before he can say what it is, Rocky opens the door and lets them out, explaining that he thought they were the ghosts of school girls haunting the bathroom. Gumball and Darwin cheer at their liberation, but as they walk away, Gumball becomes curious as to what Darwin's secret is. Darwin refuses to tell.
When they get home, they play the fighting video game. Gumball, becoming more and more frustrated over Darwin's secret, begins mashing buttons really quickly out of anger. He beats Darwin's character violently, mashing him to dust with a big, wooden hammer as Darwin looks on in shock.
Later, Gumball prepares a meal for Darwin. Darwin warily eats it, believing it to be a ploy by Gumball to get his secret. He's right - Gumball made the food extremely spicy, and made all liquids inaccessible to Darwin, except for one glass of milk that he uses to taunt Darwin. Darwin chases after Gumball, desperately trying to grab the glass of milk, but Gumball simply and gracefully dodges his dives. Eventually, he is reduced to crawling. Right when he gets into grabbing range, Gumball sets it farther, and Darwin finally passes out, a flame portruding from his mouth. Gumball, feeling guilty, douses the flame with the milk, and Darwin jumps up and thanks him. Gumball grudgingly acknowledging it.
Gumball's next plan is to pretend to be a recorded message for Darwin. Using a pay phone, he calls the house. Richard answers the phone, and summons Darwin when he learns the message is for him. Gumball convinces Darwin that he has won a prize, but to claim it, he needs to tell his secret. The prize is vouchers for a beauty spa. While Richard is ecstatic, Darwin is not pleased. At this point, Gumball's phone time is almost up, and he has run out of quarters. He tells Darwin to hurry up. Darwin begins to ask for more spa details, but Gumball interrupts him with a loud "GIVE ME THE ANSWER!". Right before Darwin tells him the secret, his phone time runs out, causing Gumball to rage.
Gumball then tries reading Darwin's mind to figure out his secret. By doing so, he tries to focus on Darwin who is drawing a picture of something. When Gumball's face stretches all the way toward Darwin, Darwin wonders if Gumball's trying to read his mind. Gumball asks if Darwin was thinking that Gumball's face hurts from his attempt. Darwin says he isn't, and Gumball decides he wasn't trying to read his mind and lets his face relax after a sad attempt with his face giving out after that.
That night, Darwin dreams about himself swimming in the ocean. He hears a crying shrimp, and goes to him, asking him if he was alright. The shrimp claims he's sad because his friend won't tell him his secret. Darwin tells him that even best friends have secrets. The shrimp asks Darwin if he has a secret, and if he does, he should tell him, so he would feel better. Darwin refuses, but the shrimp just begs him to. The dream then becomes a nightmare, as all the sea creatures (including a catfish, who lives in fresh water) come out, and ask Darwin for his secret. Darwin wakes up, only to see Gumball begging Darwin to tell him his secret. When Gumball finds Darwin awake, he rubs Darwin's fishbowl to help him sleep.
The next morning Anais claims to know Darwin's secret, and Gumball persists to get it out of her by poking at her head all day and on the bus ride to school. Anais threatens Gumball not to poke her again, but he does it anyway, causing him to get beat up. At school, Gumball acts as if he knows the secret to cleverly get it out of Darwin, however, Darwin says he'd only tell the secret in a life or death situation.
Gumball locks him and Darwin in the boys bathroom to get the secret out of him. Darwin says that the secret was the sandwich Gumball made for him wasn't great, it was only good. Shocked and angered, Gumball throws a fit at Darwin, since he expected the secret to be something less trivial. The only way out of the bathroom was through the sewers, which Gumball obviously didn't approve of. Soon enough, after minutes of swimming through sewage, arguing over the whole buildup to the secret, and ending up as a bottle of water at the water purification plant, Gumball and Darwin get home, coming up from the toilet in the bathroom, scaring Richard who was washing his hands and wonders if he ate them. They say he didn't and they were just trapped in the sewers, relieving Richard.
Darwin leaves the bathroom, letting Gumball take a shower, Anais asks Darwin if he told the real secret. Darwin says "No, he must never know that we accidentally uploaded that clip.". The video, is Gumball doing a hip hop dance and failing miserably as he destroys his whole room in the process. The video is shown to be a major hit because of the high amount of views it has received.