Young Kay Harker has a variety of adventures in search of the truth about a famous treasure that his great-grandfather, a merchant captain, was given for safe-keeping then lost when his crew mutinied. He is aided in his quest by the Midnight Folk, an association of Talking Animals, Living Toys, and other fantastic creatures.
But not all the creatures that haunt the night are friendly: a coven of witches is also after the treasure, led by the scheming Abner Brown and the sinister Mrs Pouncer, and woe betide anyone who gets in their way.
A sequel, The Box Of Delights, was published in 1935. The two books also have links, in terms of shared settings and characters, with a series of adventure stories for adults which began with Sard Harker in 1925.
This novel provides examples of:
- Abandoned Area: The brewery and stables at Seekings, obsolete in the age of mass-produced beer and motor cars, now slowly falling into ruin.
- All Witches Have Cats: Blackmalkin and Greymalkin serve the coven as familiars. Nibbins also used to be a familiar, but is now a household cat who sides with Kay.
- Ancestral Name: Several characters pass their names down through the generations:
- Abner shares his forename with his father and grandfather.
- Miss Piney Trigger has the same name as her father.
- Roper Bilges the gamekeeper shares the name of his grandfather, one of the mutineers on Captain Harker's ship.
- The Atoner: Twiney Pricker, one of the crewmen who mutinied to steal the treasure, subsequently repented and spent the last years of his life tracking it down to return it to Captain Harker. He nearly succeeded, but Abner's grandfather was too much for him.
- Black Knight: On the way to meet King Arthur, Kay, the unnamed messenger and Sir Launcelot encounter a supernatural Black Knight who treats beheading as a minor setback.
- Brick Joke: Kay's letter-writing style, which his governess scolds him about during a writing lesson early in the book, returns full-force near the end when he writes a letter to the authorities to let them know the treasure has been found.
- Character Overlap: Abner Brown previously appeared as a henchman of the villain (also a black magician) in Sard Harker. Sard Harker himself is perhaps a relative of Kay, although they're not explicitly connected (the details that are given are at least sufficient to establish that he's not a direct ancestor).
- Cunning Like a Fox: One of Kay's allies is Rollicum Bitem Lightfoot, a fox who relies on his wits to keep one step ahead of the local gamekeeper.
- Deserted Island: What with all the mutinies and maroonings, the history of the treasure includes several, each more bleak and inhospitable than the one before.
- Direct Line to the Author: The "Where Are They Now?" Epilogue includes a couple of lapses into first-person, indicating that the author lives in the neighbourhood where the novel is set and has met (or, in the case of the fox, had his poultry raided by) some of the characters.
- Finally Found the Body: The discovery of Twiney Pricker's body, near the end of the book, is what finally leads Kay to the treasure.
- Flying Broomstick: Used by the witches.
- Funetik Aksent: Twiney Pricker's Northern British accent is rendered like this.
- Gender-Blender Name: When Twiney Pricker reinvented himself as Piney Trigger, he gave the same forename (Piney) to his daughter.
- Gossipy Hens: Kay's governess's social circle includes a flock of them, with names like Mrs Gossip, Mrs Tattle, and Mrs Scatternews.
- Haggis Is Horrible: The Rat fondly recalls a time when a haggis was delivered to Kay's family but had gone bad and was thrown away — so he got it all to himself.
- Hard-Drinking Party Girl: Piney Trigger (the daughter) boasts of being one even into extreme old age.
- The Highwayman: Kay is told a tale about Benjamin the highwayman, who used to live in the area.
- Invisibility: One of the witches drops a vial of invisibility potion, which Kay makes use of. The gamekeeper's dogs can still detect him by scent, though.
- Latin Land: Santa Barbara, where the treasure came from.
- Living Drawing: Kay's family portraits come to life and talk to him.
- Living Toys: Kay's toys are among the Midnight Folk of the title.
- Meaningful Name: Meaningful to the author, at least. "Caroline Louisa" was the name of Masefield's own mother, who died when he was six.
- The Mutiny: Captain Harker's crew mutinied and marooned him so they could steal the treasure. The subsequent history of the treasure turns out to involve several more mutinies and maroonings with the same motivation.
- Narrative Profanity Filter: Whenever Roper Bilges uses a profane verb, which he does often, it's obscured by verbing the nearest relevant noun.'It sounded like a young jackdaw got down the chimney again.'
'I'll jackdaw them jackdaws one of these days,' he said, 'if they keep on jackdawing me.' - Oracular Head: The coven uses a Brazen Head that can see into the past in an attempt to locate the treasure.
- Or Was It a Dream?: Played with all through the book. All the supernatural events end with Kay waking up, but the "mundane" adventure story (where he's definitely awake) only makes sense if the things he learns on these expeditions are true.
- Parental Abandonment: Kay's parents are both dead.
- Portrait Painting Peephole: Kay uses one to spy on a meeting of the coven.
- Public Domain Character: King Arthur and his court make a cameo appearance.
- Seven League Boots: The witches have seven-league boots, as well as forty-nine league boots.
- Shout-Out to Shakespeare: Greymalkin is the name of one of the witches' familiars in Macbeth.
- Species Surname: Kay's toys include a dog named Dogg and another named P. Dogg (they're said to be cousins), as well as a bear named G. L. Brown Bear. Many of the wild animals he meets also seem to be named after their species, as Bat, Otter, Water Rat, etc.
- Summoning Ritual: Mrs Pouncer uses one to summon various supernatural entities, to ask them where the treasure might be. One of the supernatural figures that appears is a woman on a black mare who arrives unsummoned, and Mrs Pouncer has some trouble getting rid of her. She reappears at the end as Kay's new guardian, Caroline Louisa.
- Talking Animal: Many of the Midnight Folk are these.
- Two Aliases, One Character: Kay's governess Sylvia Daisy and the wicked witch Mrs Pouncer are revealed to be one and the same.
- When I Was Your Age...: Kay's governess and Mrs Tattle have a session of complaining about what young people these days are coming to, and how none of them are "what we were when we were girls". "Which," the narrator drily notes, in the case of Kay "was very likely true."
- "Where Are They Now?" Epilogue: Though not marked off as an epilogue (the book has no chapter divisions), the last couple of pages consist of a series of descriptions of what happened to various characters afterward.
- Wicked Witch: Mrs Pouncer and her colleagues, complete with familiar felines, flying broomsticks, tall pointy hats, wrinkled faces, hooky noses, etc. It turns out that the faces are cunningly-fashioned masks that come off with the hats when they return to their respectable daylight lives.
- You Dirty Rat!: The Cellar Rat is an information broker, who will happily sell out either side for green cheese or haggis.
- Your Size May Vary: The relative sizes of Kay and the various Midnight Folk is never nailed down, and seems to vary according to convenience. Whenever Kay is hanging out with animals, he's apparently about the same size as they are, and when his toys are out and about, they seem to be life-size. There is one occasion on which Kay explicitly shrinks, in order to go on a voyage in a model ship crewed by mice, but even then there are times in the voyage where Kay seems to be his normal size again and the ship and mice have implicitly grown to match.
