The episode begins as the PJ Masks return home after fighting off Romeo, Gekko upset about messing up during the battle. At the same time, Motsuki spies on the team after flying off with the moths due to Luna Girl’s Moon Whistle playing. The next day, the kids receive a letter during their galaxy lesson in class, saying that Luna Girl is planning something big. That night, PJ Robot scans the letter, and the PJ Picture Player shows the villaness playing her moon whistle. Feeling that it might be a trap, and fearing that he might mess up again, Gekko offers to stay with PJ Robot and be on the lookout for any trouble.
Catboy and Owlette take off to the park in the Cat-Car as Motsuki watches from behind. Seeing that Gekko is not with them, she goes to headquarters to present Gekko with “pizza”. He comes out, refusing to do anything with her, and she opens the pizza box to release the moths hiding in there. They carry Gekko away from the entrance, and they and Motsuki quickly enter HQ. Catboy and Owlette contact him in concern, to which he replies that he is just fixing HQ’s door.
The two soon arrive at the park and grab Luna Girl’s attention with the letter that one of the moths sent them. Luna Girl takes a closer look at the letter, and she realizes the drawings were made by Motsuki. She tells them that it was only a trick to get the PJ Masks away from headquarters. Catboy and Owlette start running back to the Cat-Car, but Luna Girl stops them and asks them to listen to her moon whistle. When they refuse, she freezes them with her Luna Magnet and resumes playing, shattering the objects within the pitch’s range.
Luna Girl finishes, and she asks Catboy and Owlette to applaud. The two ask her to unfreeze them first, which she does so. They applaud, and while she bows, they take this opportunity to run to the Cat-Car. They leave just as Luna Girl notices, and she throws her moon whistle away in anger. The two contact Gekko again, who is back in HQ after using his Super Gekko Muscles to pry open its door. He claims that everything is fine, until Motsuki shows up in the control panel’s screen.
Gekko quickly breaks off contact with Catboy and Owlette and orders Motsuki to leave. Motsuki sends the moths off in response, and they spread out in groups around HQ. One group enters the power chamber, and they mess with its controls. Gekko and PJ Robot desperately try to fix the system, when Motsuki offers to help. Despite PJ Robot’s disapproval, Gekko lets her, and she presses HQ’s rocket function, revealing that she is going to fly to the moon to make HQ her own headquarters. Gekko and PJ Robot try to stop her, but she traps them in bubbles. She then turns on the video camera, and reveals that the Cat-Car has been affected with the moths’ infiltration as well.
Motsuki suddenly notices HQ flying erratically, to which Gekko tells her it is because of her moths infiltrating its system. She calls the moths to regroup, and the controls start working again. HQ heads straight for the moon, and she releases Gekko and PJ Robot outside. PJ Robot catches Gekko as they fall, and he is placed safely to the ground, while Catboy and Owlette quickly return to HQ as the Cat-Car is also working again.
Gekko tells Catboy and Owlette what happened, and apologizes about not telling the truth earlier. They comfort him, telling him that everyone makes mistakes, and that they could have helped him if he told them about the problem sooner. Luna Girl suddenly flies by them, and she explains that she threw her moon whistle away because no likes her music. Getting an idea, Gekko asks the team to help find her whistle, and everyone returns back to the park.
In a few moments, Owlette finds the moon whistle. She gives it to Gekko, and PJ Robot flies him up to HQ as he plays, holding a speaker. Soon enough, Motsuki hears its music, and she and the moths leave the structure. PJ Robot accesses its system, and HQ returns to its proper place. Gekko and PJ Robot return, when Luna Girl takes her moon whistle away from Gekko, who comments that she threw it away. She claims that everyone makes mistakes, and she continues practicing as she flies off, while the PJ Masks proclaim their signature victory phrase.
Don't be afraid to tell the truth (it's good to be honest).
Everyone makes mistakes; nobody is perfect.
The episode's title might be a reference to the song, "Who Let the Dogs Out!".
Luna Girl introduces her Moon Whistle in this episode.