After joining the Sparrow Scouts, Hilda partners with her new pals Frida and David to clean up a park, not realizing what's lurking underground.
Hilda joins the Sparrow Scouts. The episode begins with her taking the oath, and joining the other scouts in a game of sting ball. After her initiation is complete, the Raven Leader announces the first assignment for earning a badge that year; a beautification project in Trolberg City Park. Teams of Sparrow Scouts get one weekend to clean up and improve the section of the park given to them. If successful, they will earn the Friend of the Park badge.
Frida, always eager to earn new badges, volunteers as team leader, and picks Hilda and David for her team (Hilda mainly because helping a new kid will get her points for the Level Three Friendly and Helpful Badge. They will start the following day. On their way home, Johanna tells Hilda about the many badges she earned in her time as a Sparrow Scout.
The following day, Frida and David come to pick up Hilda, and are quite surprised to see that she has a deer-fox as a pet. Frida made a detailed action plan and tight schedule to ensure the projects success. The three friends begin with removing all the unwanted vegetation, and marking the sections for new plants with stakes and rope. While they work, Frida and Hilda tease David about the many Trolls that could be on the other side of the wall. By the end of the day, the kids bring the removed plants to the Trolberg Mulching Center to be grinded up to mulch. As they leave the park however, none of them notices that the last stake Hilda hammered into the ground begins to move, and a creature rises up from underneath. They likewise fail to notice that the weeds they brought to the mulching center are actually sleeping creatures.
The kids return the day after, only to discover that all their work from the previous day has been trashed. The culprit is revealed to be a plantlike creature, with one of the stakes in his head. He attacks them with a spade, but backs off when Twig defends Hilda. The creature introduces himself as a Vittra; a race of plantlike creatures that live underground. Once a year, they come up to the surface to hibernate and catch some sunlight. The weeds the three kids removed the day before were in fact sleeping Vittra. The only reason this one Vittra woke up was because Hilda drove a stake into his head.
The Vittra doesn’t believe Frida that they didn’t hurt his kind on purpose, and steals her sash. Frida panics and follows him into the underground tunnels to get her sash back. Hilda follows Frida, ordering David to remain near the tunnel entrance with a rope to help them out. David gets distracted however when he notices an unusual rock, and it’s only thanks to Twig that the rope doesn’t fall into the hole.
The underground tunnels are quite a maze. While searching for Frida, Hilda stumbles upon a tunnel to the surface on the outside of the wall, and to her shock realizes there is a (now fortunately petrified) troll right outside the walls. She eventually manages to catch up with the Vittra that took Frida’s sash, who promises to help her find Frida if Hilda helps to return his friends. Hilda agrees. With the Vittra’s help, she finds Frida, who got stuck in a rabbit hole that she mistook for another Vittra tunnel, and helps her get free.
Back above ground, Frida apologizes to Hilda for going after the Vittra like she did. She and David agree to help rescue the other Vittra, even if this means they will fail the badge challenge. The kids hurry to the mulching center, where the sleeping Vittra have already been loaded onto the Big Chipper mulching machine. Since the center is closed, they are forced to climb over the gate. With great effort, the kids are able to rescue the Vittra. Hilda falls off the Big Chipper when rescuing the last one, but Frida and David catch her.
The kids return the Vittra to their places. The Vittra returns Frida’s sash and also retreats underground. The kids go home, and report their failure of the project to the Raven Leader the following day. That night, as David goes to sleep, the rock he found earlier begins to move.
- The scene of Hilda, David, and Frida having to rescue the Vittra from the Big Chipper was adapted into "Hilda and the Nowhere Space".