Reading Alan Garner is not a spectator sport. You have to participate quite energetically: be alert to pick up on all the clues. He doesn't do explaining. That's why some readers have been left feeling bewildered.
With that in mind, let me set the scene for The Owl Service, especially for American readers who don't have some of the background needed to pick up on the small hints he drops in the turn of a phrase. All this is established in the early chapters, but not spelt out.
The central figure is the young teenager Alison. Her father died and her mother remarried. Clive Bradley is a well-meaning but emotionally clueless man, though of course he is aware of the typical issues of stepfatherhood. He has his own son, Roger, about Alison's age. So they are an upper-middle class English family on holiday (vacation) in a house that Alison's mother (or strictly speaking, Alison) owns in a deep isolated valley in Wales and where they have a local Welsh woman, Nancy, who works for them as cook and housekeeper. Nancy has a son, Gwyn, about the same age as the others...and attracted to Alison. Then there is Huw Halfbacon who is - or appears to be - a slow-witted garden servant (why do all the villagers address him with a title of great respect?)
Now already you have three tensions established: first, the UK class thing of the householder and the servant, with differing levels of money, speech, and education. Nancy is conflicted about her "Welshness" and wants Gwyn to get out of it: she actually prefers to be in the English world, where she says "I know my place" lowly though that place is. Although she has sent Gwyn to the best local school, she doesn't like that they teach him Welsh language and history.
This leads to the next tension: the Welsh/English thing, with all its past memories of the Celtic resentment of the down-to-earth, practical, invading "English" who pushed the dreamy, poetic, magic-believing Celtic nations, with their Gaelic languages, to the western fringe of Britain, and from the 5th century onwards often treated them as tiresome eccentrics.
And finally, do I need to stress the tension of having two teenage boys and one girl. This is what brings to life the ancient curse of repetition that hangs over this remote Welsh valley, known and understood by the locals talking Welsh amongst each other in the shops: the ineluctable repetition of an ancient drama of magic, jealousy and murder.
OK. Now let's develop the characters a bit. Clive, the stepfather, is a "rough diamond." He's made a lot of money and has no patience with nuance. Wants money to resolve everything. His first wife left him - they don't talk about that, especially the son Roger. Alison's mother was criticized for remarrying so soon and possibly for money.
Nancy the cook grew up in the valley but left it following a tragedy and spent most of her life in the nearby town, Aberystwyth. Now she has returned, full of a sort of inverse snobbery and tremendous conflicts about the Welsh v. English thing. I won't go into detail on the revelations about her previous links with the house and indeed with Alison's mother Margaret, a shadowy background figure we never really see. [SLIGHT SPOILER ALERT - It turns out that Nancy's story was yet another previous re-enactment of the ancient cycle of doom...]
She is wedded to the old concepts of immutable class: the noble born and the humble are fine in their respective stations, but she despises the nouveau-riche like Clive Bradley.
Gwyn is a tremendously sympathetic character: mocked for his "country bumpkin" nature by the bigoted English, yet in fact full of ideals and dreams beyond them and in fact well-educated from the grammar school. Has a really, really bad relationship with his mother. Incidentally, again for American readers, Brits understand immediately why Nancy is "me Mam" and Alison's mother is "Mummy" and what that means in class terms.
Every time the centuries-old trapped elemental force of the unhappy Blodeuwedd, the woman made by the wizard out of flowers, finds a modern emotional situation that resembles the one of her ancient tragedy, it manifests itself through the girl of today. It can come either as a terrifying predatory presence that has the nature of a huge fierce owl, or many owls, and will go "hunting," or as a blessing of sweetness and light, with wildflower fragrances, representing the original nature of Blodeuwedd. You will have to see what happens in this wondrous book.
A few quick translations of things I suspect aren't American usage:
If someone is conning you with a tall tale, he's said to be "pulling your leg." If you suspect this, you can tell him "Pull the other one, it's got bells on" - (so more rewarding than this one.)
Packet of fags - cigarettes.
Petrol - gas
Torch - flashlight
Anorak - windbreaker
Ping-pong - table tennis
Snooker - table ball game like pool
The ab-dabs - feeling spooked
Pebble-dash - a rough stucco-type wall finish with tiny stones embedded in it
Flitch - a half-side of bacon. See the part where Huw Halfbacon explains his name.
Torch - flashlight
First floor - US second floor