Mystery with mythological elements, set on the Greek island of Serifos: Pethi, a Greek boy who's grown up never knowing his father, and Tini, an English girl whose father's an archaeologist, decipher an ancient riddle and find themselves racing towards a treasure that's lain hidden for many centuries.
Reread after about thirty years: I recall enjoying this as a child, and I'm pleased to find that it's stood the test of time. The characters are as distinctive, the plot as intriguing, the setting as vivid as I remembered.
I remembered the answer to the riddle of that title; I remembered the cat who liked to drape himself over his owner's shoulders; I remembered the gliding handmaidens. But not much else: and half of what I thought I remembered wasn't in this book at all, which means it must be in A Circle of Stones -- the book that precedes this one, which I didn't recall ever having read.
I'd completely forgotten the mythological elements, and didn't spot the resonances with a certain myth until I read the author's afterword. This is how mythic elements are best handled: strong, simple tales retold in trappings that don't give them away. If I'd known which myth the story was (partly) based upon, I would have guessed a few aspects of the ending that came as a surprise to me all over again.