Amaya, Greg and Connor visit the museum. Greg claims to love the place so much, he can locate all the exhibits with his eyes closed. Amaya and Connor take him up to the challenge, and Greg indeed correctly identifies each room. When they get to the dragon gong however, it turns out to be gone. They suspect Night Ninja took it, and decide to investigate.
That night, the three heroes meet up in HQ, and see Night Ninja and his Ninajalinos taking the dragon gong to Mystery Mountain. They use the PJ Rovers to follow the villains there. Once the PJ Masks arrive at Mystery Mountain, clouds form in the sky and it begins to thunder. They try to follow Night Ninja up the mountain, when suddenly some large boulders come falling down, blocking the path and forcing the PJ Masks to continue on foot. Then geysers of red Sticky Splat erupt, and it's only thanks to Owlette that the PJ Masks escape. Something is definitely wrong with Mystery Mountain, and the heroes are not sure if Night Ninja is to blame.
To avoid any more traps, the PJ Masks use some bamboo to catapult themselves straight to the summit. Once there, they see Night Ninja and his Ninjalinos using a scroll to place the Dragon Gong in a marked location inside the pagoda. Once it's in place, Night Ninja tries to take the mallet from the gong. It's stuck, but the Teeny Weeny ninjalino helps him out with the corresponding spell. Now with the gong and the mallet in his possession, Night Ninja reveals his plan to have the dragon break open the Pagoda, allowing Night Ninja to steal the secrets of Mystery Mountain.
The PJ Masks reveal themselves, but fail to stop Night Ninja from summoning the dragon. The Dragon doesn't seem to recognize the PJ Masks, and Night Ninja orders her to attack the heroes. The Dragon uses her dragon breath to blow the PJ Masks out of the Pagoda, but then she suddenly vanishes. Next, the doors of the pagoda open, and to Night Ninja's surprise the mallet changes into a flute. Finally, a mysterious girl shows up, takes the flute, and leaps out of the pagoda after the PJ Masks, leaving a flabbergasted Night Ninja behind.
Using her flute to control the vines and rocks on Mystery Mountain, the new girl saves all 3 PJ masks from falling, and brings them to safety in the bamboo forest. She has no time to explain who she is however, since Night Ninja still needs to be stopped. Owlette offers to help, but the girl refuses, stating this is her battle. She orders the PJ Masks to go home, then flies back to the summit. Naturally, the heroes refuse and follow her.
Meanwhile, Night Ninja and his Ninjalinos have entered the Pagoda, and already stolen its first relic; the invisibility stone. The girl confronts Night Ninja, and demands the stone back. Night Ninja tries to call the dragon to help him, but she doesn't show up. Then the PJ Masks also show up, prompting the girl to once more order them to leave. When she sees the NInjalinos inside the pagoda, she teleports away, leaving the PJ Masks with Night Ninja. Night Ninja then takes out a second stone; a red one, with the power to turn anything to stone. A brief fight between him and the PJ Masks follows. Eventually, Night Ninja uses sticky splat projectiles to trap Catboy and Gekko, and the red stone to turn Owlette's boots to stone, trapping all three. He proceeds to turn Gekko and Catboy's feet to stone as well.
With the heroes incapacitated, and slowly turning to statues, Night Ninja goes back to the pagoda, when his Ninjalinos come running out the door, emptyhanded and clearly scared. The girl chased them out. Night Ninja tries to call the dragon again, but the girl informs him the dragon is gone. He then tries to turn the girl to stone, but she dodges his attack. Night Ninja then makes himself invisible and steals the girl's staff, leaving her powerless. Despite being stuck, Catboy and Owlette manage to use their powers to take the staff back, and Gekko manages to capture Night Ninja. The girl uses her magic flute to force Night NInja to give the stones back, and turns the PJ Masks back to normal.
The girl finally reveals her true identity; she is the dragon. Night Ninja freed her when he returned the gong to Mystery Mountain. With her flute, she sends the ninjas off Mystery Mountain. When they're gone, the girl introduces herself to the PJ Masks as An Yu. She bids them farewell, and hopes to meet them again soon.
- This episode features An Yu's first appearance in human form.
- This is the fourth special episode of the series.