When David blames his nightmares on Hilda and her hair-raising adventures, she decides to try and help him face his fears.
The episode opens with David having a nightmare in which he, Hilda and Frida explore one of Trolberg’s storm drain tunnels, but get attacked by a large swarm of rats. He wakes up screaming in terror and throws his stuffed bear, Warren, out of bed.
That morning, Hilda and Frida come to pick him up. Frida suggests they go for a bike ride, but Hilda dismisses the idea. She’d rather explore mysteries of the outside world, like who the mysterious girl that is hanging out in front of David’s house is. Frida explains Hilda that in the city, it’s quite normal that you don’t know everybody. Hilda is not convinced and tries to follow the girl, but she vanishes without a trace after entering an alley.
David confesses to his friends that he’s been having nightmares all week, and he thinks Hilda is the cause since she constantly drags him along in her dangerous adventures. His latest nightmare is, according to him, inspired by Hilda’s tales about the Rat King. Feeling sorry for David, Hilda promises to help him; by finding the Rat King so David can see he’s not as scary as he thinks.
So, just like in David’s nightmare, the three friends enter a stormdrain tunnel. They are caught off guard by a flood and flushed deep into the sewers of Trolberg. Here they meet the Rat King, who, just like Hilda predicted, turns out to be not as hostile as David feared. He is just interested in trading secrets. In return for a secret of her (which the viewer doesn’t get to hear), the Rat King tells Hilda that the teenage girl they saw earlier is causing David’s nightmares.
Armed with this new information, Frida, Hilda and Twig spend the next night watching David’s house. They see the teenager again, and discover she has powers; she can teleport in a green mist. Despite this, Hilda, Frida and Twig manage to follow her to the Huldrawood outside the city, where more teenage girls with similar powers are gathered around a campfire. The girl they followed is sharing a story about a nightmare David had. Hilda tries to confront them, but they all teleport away.
The following day the three friends visit the Library, and discover the teenagers they saw are Marra; evil spirits that give people nightmares. They can be warded off by strapping yourself in bed with a leather belt, but David declines this option since he fears belts. Instead, Hilda decides to switch places with David for the night so she can talk to the Marra. The two friends disguise themselves as each other, and go to each other’s homes. Frida and Alfur also spend the night in David’s room with Hilda.
The plan works and the girls manage to capture the Marra with a belt. The Marra admits she likes to prey on David since he has so many fears to make nightmares with. Hilda scolds her for picking an easy target, and challenges her to try and scare someone who isn’t so easily frightened; Hilda herself. The Marra accepts the challenge. She starts with giving Hilda dreams about spiders invading her home, her mother becoming evil, and getting attacked by a forest giant, but all to no avail. Then the Marra however starts to use Hilda’s only fear; her inability to ride a bike (and her not wanting her friends to find out she can’t ), giving the girl a nightmare in which she's riding an out of control bike, and getting attacked by sentient cars.
Meanwhile, in Hilda’s house, Johanna discovers that David is the one sleeping in Hilda’s bed. She brings the boy home. There, David sees Hilda struggle with the nightmares caused by the Marra. Unwilling to let his friend make this sacrifice, he offers to take the Marra back.
The following day David admits he didn’t have any nightmares again. The Marra also shows up, and confesses she gave up on David since it’s no fun getting nightmares from a willing victim. She admits she learned Hilda’s secret about bikes from the Rat King (this is the secret Hilda told him earlier). The episode ends with Hilda asking Frida and David if they can teach her how to ride a bike.
- Rat King
- Woff (in Hilda's dream)
- Forest Giant (in Hilda’s nightmare)
- Jellybean (cameo on a poster on a wall).
- The episode was adapted into "Hilda and the Nowhere Space", but the adaptation leaves out the Rat King and combines the plot with the Marra scenes from "Chapter 12: The Nisse".