On one peaceful night, Hilda and her mother receive a tiny letter from a mysterious group telling them to move out or face the consequences. Hilda, annoyed, sends the senders back a letter telling them they won't move out.
Things take a turn for the worse, however, as Hilda and her mother get their house attacked by the tiny people later that night, convincing Hilda's mum to move out of the wilderness and to the city, much to Hilda's dismay. The day after the attack, Hilda soon meets one of those mysterious tiny people, Alfur, who reveals to Hilda that he is an elf, a race of people hidden from humanity unless they sign a contract. Furthermore, Hilda learns that these elves view Hilda and her family as a threat due to the former unwillingly stepping on the latter's homes. And so, Hilda, teaming up with Alfur, sets off on an adventure to convince the leader of the elves that she and her mom are harmless and to allow them to stay.
On the same night of the attacks, Hilda also discovers a mysterious giant who comes around their house at night, causing the curious adventurer to seek him out, figure out who he is, and why he is coming to their home every night.
The book would be followed up by Hilda and the Bird Parade. The Midnight Giant, alongside parts of Hilda and the Troll would be adapted into the first two episodes of the 2018 series. It would also receive a novel adaptation as part of the Hilda Tie-In Series under the title, Hilda and the Hidden People.
The Midnight Giant provides examples of:
- All There in the Manual: The final two pages of the graphic novel contain an overview of 20 giants, including their names and a brief history.
- An Ice Person: Among the 20 giants listed in the final pages are three that are made of ice and snow: The Ice Man, Kald the Winterbringer, and her brother Drib.
- Arboreal Abode: Wood Man lives in a house that is build around, and partly inside, a hollow tree.
- Attack of the 50-Foot Whatever: Actually subverted with the Midnight Giant itself. It's more of a "conversation with a fifty foot whatever" than anything really. He even has a proper name: Jorgen.
- Big Little Brother: The giant Kald was many times larger than her older brother Drib.
- Bittersweet Ending: The Midnight Giant and his girlfriend are reunited. But in their joy, they are blissfully unaware that they crushed Hilda and her mum's house, forcing them to relocate and rendering Hilda's efforts to be All for Nothing. However, Hilda brings back the idea of moving to the city, citing how it's not so quiet in the outside anymore.
- Brick Joke: When Hilda confronts the Mayor of the Hidden People, his fat cat sneaks into Hilda's hair. After Hilda uses this to her advantage to find out where the Prime Minister is, the cat ends up all skinny.
◊ Much later, when Hilda feels itchy and thinks she has nits, it turns out the cat gave birth to kittens (or nittens)◊. - Colossus Climb: Hilda climbs on Jorgen with help of a Woff so she can talk with him. Later, the mountain she climbed to get to the Elf King also turns out to be a giant.
- Dark Is Not Evil: Among the giants listed on the final pages is Myrkr; a giant that looks like a big shadow with eyes. According to his bio, he was associated with ill health and bad omens, but was actually terribly nice.
- Franchise Codifier: Luke Pearson considers this book to be the point at which the Hilda series truly begins to develop its own identity, as it moves away from Hildafolk's breezy and incidental Moomins-inspired tone and establishes the tone, atmosphere, and story structure that would define the series going forward.
- Genius Loci: The Knolem is a "mean-spirited, living hill".
- Gentle Giant: The eponymous Midnight Giant, as it turns out. This detail is also attributed to several of the other giants, most notably Halldor, who is said to have been on good terms with humans and very fond of them, and Gertl, who is described as "the most fun to be around". Averted by Fjallmarr and the Knolem, who are described as having been actively hostile to humans.
- Green Thumb: One of the giants detailed in the last two pages is Valfreyja, who is said to have planted the forests of the setting.
- Invisible to Normals: The elves and their houses. Evidently, you can see them just fine as long as you fill out the proper paperwork.
- Long-Lost Relative: The foldout detailing the giants at the end of the book reveals that the Midnight Giant had a cousin named Sigmund, who resembles a red-furred version of him, albeit shaggier and with horns.
- Meaningful Echo: After the house gets attacked by invisible elves, Hilda's mum tries to tell Hilda some of the perks of moving to the city. Much later on, when everything is said and done and their house gets crushed, Hilda uses the same perks that her mum used regarding moving to the city.
- Monster Progenitor: Two giants detailed in the final pages, Fjallmarr and Bjorg, are described as the ancestors of some of the magical creatures in the setting, namely dragons and nisse (neither of which had been properly introduced into the Hilda universe at the timenote ). And in a different manner, many of the more unusual and inexplicable creatures in the world of Hilda are said to have been born of Har's beard.
- Multiple Head Case: Among the giants detailed in the last two pages is Jadarrok, who possesses seven heads stacked willy-nilly on top his shoulders. He's noted as being a loner, since for him, having six extra heads is company enough.
- No Name Given: The Midnight Giant's girlfriend is never identified and neither is she included amongst the giants in the final pages. Later material would dub her Illus, however.
- Our Giants Are Bigger: The book features a two-page image depicting the giants of old, all of whom vary greatly in size. The smallest are the Forest Giants and Blioa, followed by giants like the Knolem, Brekkus the Thunderworm, and Einarr, who barely reach up to Jorgens’s knee. Gertl is next, being about two-thirds the size of Jorgen. Then there's Jorgen and other giants as tall as him, such as Heimskr and Aldinn. And topping it all off is Har, a giant so big he dwarfs every other giant on the page, and whose head is not even drawn as he is simply too big to fit.
- Puppy-Dog Eyes: Hilda uses these on her mum after she brings up the suggestion that they'll have to move.
- The Reveal: The nearby mountain turns out to actually be not just a giant, but the Midnight Giant's girlfriend.
- "Shaggy Dog" Story: After everything Hilda did to get back on good terms with the Elves and thus be allowed to stay, it’s all rendered useless when her house is destroyed and she has to move anyway.
- You Can't Go Home Again: Mostly because your house accidentally got crushed by giants.
- Youthful Freckles: Hilda has these, but they don't appear in any of the later books...nor were they there in the first book.
