The "service" of the title refers to a set of tableware found in a musty attic, not any sort of business enterprise. A pastiche upon one of the myths of the Welsh Mabinogion, The Owl Service will seem lifeless and maddeningly obscure to anyone not versed in those stories. As with a lot of Garner's work, I've seen folks who are acquainted with his references describe this as a masterpiece. I'd dispute that, I'm afraid, as a masterpiece ought to be accessible and entertaining in its own right, whether the reader were familiar with the Mabinogion or not. The Owl Service is neither.
Set in the Welsh countryside, the book gets off to a promising start but quickly dissipates. The dinner plates are discovered by some youths following what sounds like some very intelligent rat scratching (they answer to knocks) coming from above the ceiling of a cottage. It turns out that the plates — which bear curious drawings of leaves and owls — are linked to an olde local legend about a young girl who was magically brought to life out of flowers, and how she spurned her lover for another man, leading to the expected tragic confrontation. (The aforementioned Mabinogion ref.) The problem arises when Garner, having established this legend, fails to follow through. Is the owl service linked somehow to our modern day heroes: Alison, the stepdaughter of the cottage's owner, and Gwyn, a local boy who knows lots about the legend, who are tap dancing around each other in an unrequited love? Who knows? We are told that the flower-girl from the legend is returning, but she doesn't. We never even find out what was doing the scratching in the attic. Indeed, all of the fantasy elements of the story seem to vanish as the novel progresses, leaving us to deal solely with the bland interplay between Alison, Gwyn, and other characters in the present. Garner's story is long on atmosphere, but so short on story substance that it ends up bearing more than a passing resemblance to a dream: eerie, intriguing, illogical, and almost entirely forgotten once it is over.