Read by Candlelight/Flashlight : The Weirdstone of Brisingamen, Alan Garner
Alan Garner has written some of the best fantasy books for young adults. And Philip Pullman, Neil Gaiman, Garth Nix, and Susan Cooper have all cited him as having a big influence on their work. Like them, his books have children from our world encountering creatures and people who they thought only existed in the imagination.
"Neither Susan nor her brother, Colin, ever thought that war would be waged over a simple gemstone in her bracelet. But that's what happens when the children visit Alderley Edge, a spooky place in a remote part of England. There, they meet the wizard Cadellin, who needs the stone to rouse his allies in the never-ending battle between good and evil. But when the stone vanishes, Susan and Colin must find it before the forces of evil use it to destroy all the goodness that ever existed in the world."
Garner uses a mix of Celtic and Norse folklore and mythology, so there are plenty of references to Herne the Hunter* and the Wild Hunt, the Morrigan, Brollachan et al. There are cameo appearances by characters from the Arthurian legends, and a 'blink and you'll miss it' mention of the Tarnhelm.
The Weirdstone of Brisingamen was Garner's first novel and it was published in 1960. This is what my much-loved copy (from the 1970s) looked like.
I haven't read this book in about 40 years, and I think it has held up pretty well. It's a bit creaky in places (Garner himself said it was "a fairly bad book"), but it has all the fantasy elements you could want. Wizards, elves, dwarves, scary creatures, and human children who don't have a great deal of adult supervision. All culminating in a big Good vs Evil showdown.
And reading it by candlelight has brought back many happy memories of reading this one by torchlight (I'm English, it's a torch not a flashlight) under the covers after my mum had turned the light off in my bedroom.
* Not to be confused with Herne the Hunted, who appears in Terry Pratchett's Discworld series. He is a small god and the patron of those animals destined to end up as a "brief, crunchy squeak."