Conversation so far:
What is Elidor?
Elidor is a children's fantasy novel by the British author Alan Garner, published by Collins in 1965.
When did Alan Garner play Elidor on the radio play?
In 1962, Alan Garner began work on a radio play named Elidor, which would result in the completion of a novel of the same name.

Question: What is The Owl Service?
Self-contained rewrite: What is The Owl Service?