Jake must enter the Monster World in order to recover his portable Troop Grid that allows him to close portals. Meanwhile, Hayley and Etienne pretend there is a gas leak to keep the Portal from being exposed, however other people gather around thinking that a popular band called Gas Leak is going to perform.
Plot
Jake, Hayley and Etienne arrive at an alleyway where Etienne has cornered a pair of Basilisks. The Basilisks escape the alleyway, turning two passing joggers to stone. Jake tricks the Basilisks into seeing their reflection in the windows of a bus shelter, turning them to stone. Just then, Hayley receives a Troop Grid alarm that a portal to the monster world is open. When Jake, Hayley and Etienne arrive at the portal, they find that it has not yet closed like portals usually do.
Mr. Stockley arrives, and upon viewing footage (from the previous episode) of Cadence being sucked into the monster dimension with Jake's portable Troop Grid, he explains that the Troop Grid's unique frequency is likely what is stopping the portal from closing. Jake decides to go through the portal into the monster world to retrieve the Troop Grid, and is given five vials of Dimension Mites to use to send messages back to the Troop in the human world, as well as several weapons to defend himself. Jake then goes through the portal, and finds himself in a vast, purple, underground cavern.
After spotting a light, Jake climbs up towards it and through an exit into a misty, alien forest. While exploring the monster world, coming across a trap in the ground that eats him and then releases him through another trap above, he finds Cadence's abandoned jacket. He searches for Cadence, and after sending a message back to the human world, he finds a clutch of eggs, and, feeling hungry, tries to eat one. This causes a Two-Headed Zylork to attack Jake. However, before it can kill him, Cadence appears in her Blood Thrasher form and defeats the Zylork.
Cadence tells Jake to return to his world, warning him that if he stays in the monster dimension, he will be destroyed by the monsters. Jake explains that there is a portal open, and he needs the Troop Grid Cadence grabbed in order for the portal to close. After some arguing, Cadence takes Jake to a crude hut, and reveals that she spent most of her childhood in the hut, alone. She then gives Jake his Troop Grid back and orders him to go back to his world now that he has what he's looking for. Just then, the hut comes under attack by monsters, which Cadence explains are drawn by Jake's scent, and won't stop until they get him.
Meanwhile, back in the human world, Hayley and Etienne put up a gas leak tent around the portal so that no-one sees it. When a passing girl notices the gas leak tent, she becomes strangely excited and runs off to tell her friends, leaving Hayley and Etienne confused.
Later, the girl returns with a crowd cheering "Gas Leak!" Etienne then discovers that the girl and the crowd think him and Hayley are a band called Gas Leak that shows up in random places for surprise concerts. While Etienne draws the crowd's attention, Hayley tries to stop any monsters crossing through the portal from the other world, and the crowd mistakes her pulse blasts and the light from the portal inside the tent for light effects. Eventually, Etienne plays for the Gas Leak fans with a keytar to keep the Gas Leak illusion up.
Back in the monster world, tentacles attack Cadence's hut and begin to break in, dragging Jake off. Cadence reluctantly abandons her hut to save Jake from the tentacle. After she saves him, Jake and Cadence flee as Cadence's childhood home is destroyed by the tentacles. Jake then sees that when the tentacle grabbed him, it broke his Troop Grid, meaning that the portal will now close, but also that Jake will now be trapped in the monster world.
Back in the human world, while Etienne performs to the fans, the portal begins to close. Hayley jumps through the portal, which then closes as the tent around it is blown away. When Etienne and the Gas Leak fans see this, the fans mistake it for a stunt and cheer at Etienne, who then faints.
Later, Etienne returns to Troop HQ, covered in kisses and his fake Gas Leak uniform torn from the Gas Leak fans. Mr. Stockley explains that Troops worldwide are on highest alert, and that with the portal gone, they will have to find another way to bring Jake and Hayley back from the monster dimension.
Back in the monster world, Jake and Cadence are running through the forest from the monsters, when they run into Hayley. Jake and Hayley are glad to see each other (until Jake realizes that Hayley has no way of getting them back to their world), but Hayley is immediately suspicious of Cadence due to their last encounter. Just then, the three are chased by several monsters which corner them at the face of a cliff.
In the human world, Troops across the globe, including Etienne and Mr. Stockley, prepare to initiate a plan in which each Troop will use Dimension Mites to open a portal. Jake and Hayley will have one minute to find one of these portals and cross through back into the human world before the portals close.
In the monster world, as the monsters close in on Jake, Hayley and Cadence, a portal opens up, but the monsters are between the three and the portal. At the same time, Etienne and Mr. Stockley wait for Jake and Hayley to cross through the portal they have just opened. Back in the monster dimension, Cadence draws the monsters' attention while Jake and Hayley sneak past them to the portal. But just before Jake and Hayley can escape through the portal, Cadence is injured by the monsters, so Jake and Hayley go back to rescue her. Jake, Hayley, and an injured Cadence, run for the portal, pursued by the monsters, and jump through.
At the same time in the human world, the portal Etienne and Mr. Stockley have opened closes, along with all the other portals Troops worldwide have opened. Just when all hope is lost, Etienne and Mr. Stockley are contacted by Jake, Hayley and Cadence from the Hawaii Troop's HQ; the portal the three crossed through was the one the Hawaii Troop had opened, not the one Etienne and Stockley had opened.
Later, Jake, Hayley and Cadence return to Lakewood from Hawaii, and Mr. Stockley gives Cadence several books on meditation which should help her control her monster side. Etienne then arrives, and reveals that there has been overwhelmingly positive fan reaction to Etienne's Gas Leak concert on the internet, but then realizes that no-one even knows that it was him. With Kirby having been recently freed from the time machine, Mr. Stockley allows Jake and Hayley to Snark Etienne, but not before Hayley kisses him on the cheek.
