Picking up where Chapter 13: The Stone Forest left off, Hilda has turned into a troll and is being chased by Trylla.
Scared, and still not fully aware of what happened, she flees from the Stone Forest, while Trylla tries to warn her about the sun.
But since it’s day, the sun instantly petrifies her.
In Trolberg, Johanna has great trouble controlling the now human Baba.
After Tontu decuses Hilda and Baba have been swapped, Joanna sets out to try and find the Stone Forest. But all they find are petrified trolls.
Meanwhile, Erik Ahlberg gives a press conference where he announces a curfew, as well as increased anti-troll measures, due the increased troll activity in the area.
David’s parents believe everything, but David knows Ahlberg tells only lies about the Trolls.
He meets up with Frida, and the two wonder where Hilda is.
Their class is forced to watch a highly inaccurate Safety Patrol video about trolls.
Frida's protest on the video, and actually gets support from several students.
As night falls, Johanna encounters some Safety Patrol officers, belling the petrified trolls. They order her to go back to Trolberg.
One of the trolls they belled is Hilda. With the sun set, she awakens.
And learns firsthand how hurtful bells are to trolls.
The belltowers around the city prevent her from going back there.
When fleeing, she stumbles upon a cave with tons of bells in front of the entrance.
Inside, she finds a giant, blind troll named Trundle.
Hilda finally realises she is a troll now. Trundle offers to help her if she helps him first.
He also instructs her to go back to Trylla. As long as Hilda is a troll, Trylla is her mother and will protect her.
Just like how Johanna now has to take care of Baba.
Hilda feels like a sound is calling toward Trolberg. Trylla claims all trolls feel it, hence why they stay so close to the city.
The urge to get to the source of the sound also makes several trolls quite aggressive.
The Safety Patrol has a new weapon to fight the trolls. Ahlberg is eager to test the handheld prototype.
The news that the Ahlberg has this weapon scared Johanna, as she fears for Hilda’s safety.
She tries to find Hilda again, using Hilda’s scarf and beret on every petrified troll.
But she is forced to hide when Erik Ahlberg and Gerda Gustav show up. Erik notices a crack in the rocks and plots to find his way to the inside of the mountain.
Frida and David at a protest against the Safety Patrol, and even get support from Mrs. Hallgrim.
But David quits when he spots his mom, in a Safety Patrol uniform! She has volunteered to become a bellringer.
Then they run into Baba, who had escaped Tontu’s attention, and Tontu.
Tontu brings the two kids up to speed about what happened.
David asks her if Hilda could turn back using her magic.
They turn to Kaisa for help, but she informs them Witch Magic cannot counter Troll Magic. Frida secretly borrows a book about body swap spells.
That night, Hilda and Trylla join some trolls for breakfast.
Hilda prefers something vegetarian, but the only option appears to be a sentient carrot creature.
Until one troll offers her a cup of Troll Mead; the drink Trundle asked for. Hilda runs off to give it to him.
Trundle now wants her to remove the bells that keep him trapped in the cave.
Johanna is still searching for Hilda, and finds Trylla, but she fails to catch up to her before Trylla retreats into the Stone Forest and closes the entrance.
Then she comes under attack from 3 aggressive trolls.
Alfur and Cedric distract them, but Cedric gets eaten the process.
Deep in the Stone Forest, Trylla uses her magic to tell Hilda the story of the Mountain King.
He plotted to attack Trolberg with an army of Trolls, but was opposed and defeated by Trolls who didn’t like this idea.
David and Frida's attempt on the body swap spell, but it gives them quite some trouble.
For a moment, the spell shows them Hilda as a troll.
But then the whole thing goes haywire. Witch magic and Troll magic indeed don’t mix.
Trylla shows Hilda various Trolls and their hoards, including a troll who collects soft furnishing.
It seems Hilda actually begins to like being a Troll, and the powers it gives her.
But still, she longs to be human again. Trylla realizes she made a mistake, but does not know how to reverse the spell.
Hilda thus decides to keep helping Trundle. With pillows from stolen from other Trolls hoard, she silences and removes the bells.
Frida and David on their way for Johanna to help find Hilda, but she turns them down, not wanting to endanger them.
Instead, she asks Erik Ahlberg for an escort, promising to show him the entrance to the Stone Forest. Erik eagerly accepts her.
He gives Gerda full command over the Safety Patrol during his absence, which means she has no time to help Frida and David.
Out of other options, to search for Hilda themselves.
Trundle sends Hilda on her last errant; to get him a big, red orb from the ruins of the Mountain King’s castle.
When she touches the orb, it shows her a vision on which she is human again, and is attacked by tiny trolls…
…until a giant Johanna emerges from the ground to defend her.
When the vision is over, Hilda prepares to bring the orb to Trundle.
But she is caught in the act by a giant troll.
Outside, Erik easily fights off trolls with his new torch gun, clearing a way for Johanna.
Baba opens the entrance to the Stone Forest.
Just in time so Hilda could leave the caves.
Followed by the giant troll
When she sees her mom is in danger, Hilda attacks the giant…
…and makes him fall into a ravine.
Reunited at last. Hilda takes her mum, friends and the orb to Trundle.
Trylla follows them and is shocked to see the bells to the cave are gone.
Erik attacks, thinking Hilda is dangerous. As Hilda hides, something happens to her and Baba.
The spell is broken. Baba becomes a troll again and bites Erik, who throws her away.
Hilda is human again, albeit without her clothes. Good thing Tontu brought spares.
Trylla warns Hilda that the cave is the prison of the Mountain King.
And the orb was his missing eye. Trundle breaks out of his prison.
And resumes his war on Trolberg along with his followers.
David distracts his mom so Frida can sneak out of the city. He tries in vain to tell her what the Safety Patrol does is wrong.
Frida using her magic to make a mental connection with one of the attacking trolls.
And sees the same vision Hilda saw…
…but with her own mom as the giant, who calls for her as well..
When the connection is severed, the troll attacks Frida. David buys her some time by ringing the bell.
Trundle throws a rock at the belltower and almost hits David.
But David is saved by the giant troll from earlier, who is revealed to be Trundles’ brother.
Trundle has the other trolls restrain him.
He then destroys the bell towers.
The Safety Patrol arrives to fight off the attack with their latest weapon, the Troll Buster cannon.
Trundle breaches the wall, paving a path into the city for the trolls. Trylla, Johanna and Hilda can only watch.
David's mum tries to stop David from going
Hilda was with her friends and learnt from Frida what she saw during the mind connection. She begins to understand it has something to do with Trundle’s plan.
Erik resumes control of the Safety Patrol and orders Gerda to attack Trundle with the Troll Buster. Trundle doesn’t seem to mind.
Hilda urges Erik to cease the attack, fearing that this is exactly what Trundle wants and it will mean the end of Trolberg. Gerda is willing to listen, but Erik is not.
He fires the Troll Buster
This immediately triggers an earthquake. Something is awakening underneath Trolberg.
Since Erik still won’t see reason, Hilda uses Trundle’s eye on them.
And shows him the same vision she saw, but with his own mom as the giant.
Erik orders the Safety Patrol to stand down and let the trolls into the city. The earthquake stops.
The trolls stop at the center of the city, and they suggest Frida to use her magic to find out what it is that was drawing them here.
The giant from the vision is Amma; the mother of all Trolls. She is sleeping under the city, but would have woken up and leveled everything had her children been harmed by the Safety Patrol.
Now that the trolls can finally get near her again, they sprout flowers all over their bodies.
With the crisis averted, Erik Ahlberg is given a medal, and promptly retires from the Safety Patrol.
The city introduces the Night of the Trolls as an annual event, though not everybody approves.
Baba and Hilda sometimes visit in Trolberg.
While Hilda sometimes visits Trylla and Baba in the mountains.