The book is published both as paperback and hardcover.
Newly initiated into the Sparrow Scouts, Hilda is ready to explore and document the wilderness, and perhaps even make some human friends. Yet as luck would have it, there is a dark, menacing creature afoot near Trolberg, and Hilda is whisked back home to safety. Even so, intrigue seems to follow our blue-haired heroine wherever she goes, and it seems we may finally discover why so many socks in Trolberg seem to lose their mates.
It's been six months since Hilda moved to Trolberg. She has since joined the Sparrow Scouts, but while she enjoys being a member, she has so far failed to earn any badges due to a series of misfortunes. Like one time when she, David and Frida once almost got a group of Vittra grinded up into mulch while cleaning up Gorrill Gardens. Tonight though, Hilda hopes to finally get her first real badge during Sparrow Scouts camp. Around the same time, the news in Trolberg begins to report about sightings of a large, black hound, but Hilda dismisses it as rumors.
While walking home from grocery shopping with David, Hilda encounters a homeless Nisse, who calls himself Tontu. Against David's warnings, she tries to help Tontu by taking him home, where Tontu introduces Hilda to Nowhere Space by taking her there. Unfortunately, there is already another Nisse living there (whom Hilda nicknames Baldy because of his bald head), and he doesn't like the intruder. Both Nisse end up fighting until Johanna gets home and banishes Tontu. Hilda herself barely avoids getting grounded and thus missing camp.
At the camp, Hilda's bad luck when it comes to badges continues; when setting up her tent, she ends up hammering a spike through the head of a sleeping Vittra, and the creature causes the tent to collapse. Later, when Hilda and Frida are collecting wood for the campfire, they run into Tontu again. Feeling sorry for him, Hilda gives him her firewood. That night, as the scouts sit around the campfire, David admits to Hilda that he's been having nightmares all week, and fears he'll have more tonight. When everybody is asleep, Hilda sneaks away from camp to bring Tontu some food. Instead of Tontu, she finds a group of teenage girls sitting around a campfire in the woods. They are Marra, and Hilda hears one of them bragging about the nightmares she gave David. The Marra find Hilda spying on them, but run off when the Black Hound suddenly appears and frightens them. Hilda herself is forced to hide in a hollow tree to escape the hound. She is found sometime later by Raven Leader, and this escapade officially costs her the camping badge. With the Black Hound having been seen near the camp, Raven Leader decides to send everybody home early.
The following day, Hida, Frida and David meet up at the library, where Hilda tells David about the Marra. After learning more about Marra from a library book, Hilda comes up with a plan. That night, she and Frida go camping in Frida's backyard, but in reality, David is the one sleeping in the tent while Hilda takes David's place in his bedroom to catch the Marra with a leather belt. Alfur also comes along to stand guard. The plan works, but the Marra is unwilling to let David go. So Hilda tricks the Marra into trying to give her a nightmare. The Marra's first attempts to scare Hilda with spiders and a forest giant are unsuccessful, but then she finds Hilda's fear; her inability to ride a bike (hence why she insisted on walking when she and David when grocery shopping earlier). David, unable to see Hilda suffer for him, comes back to his room and confronts the Marra. He is willing to take her back if she leaves Hilda alone. Disgusted by this display of friendship, and because it's no fun to scare people that ask for it, the Marra decides to leave David alone from now on.
Hilda, inspired by David facing his fear, decides to do the same and lean to ride a bike. So early in the morning, while Frida is still asleep, Hilda takes her new bike for a ride, and after a rough start finally manages to ride it. While riding the mostly deserted streets, Hilda hears from a newspaperman that a traffic warden has been eaten by the black hound. Not much later, Hilda spots the black hound and decides to follow it. She writes a note to her mom and asks Twig to deliver it. While following the hound, Hilda sees more homeless Nisse. The chase takes Hilda out of Trolberg and into The Great Forest, but there she loses sight of the beast, and then gets lost herself.
She eventually stumbles upon the Wood Man, who is playing poker with a group of Elves. Instead of helping her like she hopes, the Wood Man ends up betting Hilda in the game and loses her to a Forest Giant. The giant takes Hilda to a hollow iron pine tree where he stores all the items he collects. When the giant is gone for a moment, Wood Man shows up at the tree and admits he lost Hilda to the giant on purpose in hopes that she can help him reclaim some of his belongings which he lost to the giant in previous games. Following Wood Man's instructions, Hilda finds a rope ladder among the giant's loot and lets the Wood Man into the tree. The giant catches them in the act, but Hilda distracts him by using some bellows to blow a cloud of dust in the giant's face. Wood Man and Hilda are eventually able to escape from the giant by hiding in a hole under the roots of a bristlecone, which turns out to be the Black Hound's lair.
Hilda quickly asks Wood Man to draw her a map so she can find the hole again, and returns to Trolberg so she can tell the police about her discovery. However, the Black Hound case has been handed to the Trolberg Safety Patrol, and since they have no authority outside of Trolberg, they can't go to the Black Hound's lair in the great forest. Frustrated, Hilda returns home. On her way there, she sees another Nisse getting evicted from a house by an old woman. She accuses the Nisse of having vandalized her living room, but the Nisse claims he's innocent, and that an earthquake or whirlwind caused the damage. The woman doesn't believe him.
Later that day, the Sparrow Scouts hold their badge ceremony, and Hilda still doesn't have the courage to tell her mom she has no badges. During the ceremony, Hilda discovers Tontu has made a new home in the Scout Hall's nowhere space. As expected, Johanna is very disappointed to find out Hilda has no badges. While guest speaker Emil Gammelplassen closes the ceremony with a poem, the Black Hound suddenly enters Scout Hall through Nowhere Space, causing panic among all those present. Tontu comes to Hilda's aid and pulls her into Nowhere Space, but the hound chases after them. Chased by the hound, Hilda and Tontu leap between the nowhere spaces of various buildings, until they end up at Hilda's house. There, Baldy confronts the hound, since it's his house too, and promptly recognizes the beast as his old pet Jellybean. He explains to Hilda and Tontu that Jellybean is a barghest, and that he found him as a puppy. He took care of him for a while, until his parents found Jellybean and returned him to the mountains. When Hilda informs Baldy that Jellybean ate a traffic warden, Baldy makes Jellybean vomit her out. Hilda realizes that Jellybean got all those nisse framed for vandalism when using Nowhere Space to navigate around Trolberg.
Johanna returns home and apologizes for being mad at Hilda. Unfortunately, the Safety Patrol has managed to track Jellybean to Hilda's house thanks to the traffic warden and Hilda's downstairs neighbor. Jellybean flees from the house onto the street, where he is cornered by the Safety Patrol. Since the Safety Patrol only has authority inside Trolberg, Hilda convinces her mom to lure Jellybean out of the city. Along with Tontu and Baldy, they get in the car and race towards the city gate, with Jellybean in close pursuit. Before they reach the gate, Jellybean catches up with the car and jumps on top of it, sending the car out of control. To avoid a crash, the two Nisse send the car and everyone in it into the Nowhere Space of the outside world; a large void. After a few seconds, Hilda, her mom, and Tontu emerge from the void in a muddy field, but Baldy and Jellybean are gone. According to Tontu, they could be anywhere now.
That evening, Hilda receives a homemade badge from her mom for helping Tontu and Jellybean, and all the other things that make Hilda unique (and thus, for which there is no badge). Tontu has come to live with them now that Baldy is gone. Alfur is excited about all the missing paperwork that could be found in Nowhere Space, while Hilda can't wait to go exploring now that she can ride a bike. The story ends with Hilda planning to go camping with Frida and David.
- Johanna (Called “Mum” in this story)
- Raven Leader
- Ms. Hallgrim (cameo in Hilda's nightmare; she mocks Hilda from within a bell tower.)
- The Librarian
- Trolberg Safety Patrol
- Emil Gammelplassen
- Wood Man
- Woff (in Hilda's nightmare)
- Troll (cameo in Hilda's nightmare, riding a unicycle)
- Lindworm (cameo in Hilda's nightmare, riding a taxi)
- Ghost (cameo in the wilderness)
- Forest Giant (both in Hilda's nightmare and a real one)
- David's Marra (simply named “The Marra” in this story)
The book combines characters and plot elements from the episodes "Chapter 4: The Sparrow Scouts", "Chapter 6: The Nightmare Spirit", "Chapter 11: The House in the Woods", "Chapter 12: The Nisse", and "Chapter 13: The Black Hound".
Like the previous book, the novel rearranges the order in which these events happen compared to the animated series, and takes several other liberties with the episodes it adapts. Included:
- In the series, Johanna is the one who warns Hilda against talking to homeless Nisse. Here, it's David. David's dialogue is pretty much the same dialogue that Joanna uses in the episode.
- Hilda does not encounter the Vittra at Sparrow Scout camp in the series.
- The novel leaves out a subplot of Frida almost joining the Marra, the plot involving the The House in the Woods, and a subplot of Hilda, David and Frida collecting stuff for the Sparrow Scouts jumble sale.
- In the series, David is with Hilda when she encounters the Marra during the night of the camp.
- In the series, David and Hilda switch houses for a night with David sleeping in Hilda's room, instead of the camping plot.
- In the series, Hilda's fear for riding a bike is only a plot point in “Chapter 6” and never mentioned again. Here, it is a subplot throughout the entire story, with her overcoming the fear in the end.
- The Rat King is absent in the book, and as such it is unknown how the Marra found out about Hilda's fear for riding a bike.
- In the series, Hilda ends up in the great forest after falling off a Weather Spirit that had had taken her from Victoria Van Gale's collapsing weather station.
- Hilda never finds the Black Hound's lair or tries to tell the authorities about it in the animated series. In fact, the series doesn't even reveal if the hound has a lair in the Great Forest.
- In the series, Hilda takes Tontu to Scout Hall and suggests he checks out the nowhere space there.
- In the series, Alfur is the one who identifies Jellybean as a barghest.
- The book doesn't reveal where exactly Baldy and Jellybean end up after escaping the nowhere space of the outside world, while the series shows them ending up near the ruins of Hilda's old house.