Its been a while since I read it, but I think it's set in a village by the coast where there are very few women, and haven't been for many years, because of a rumour that a mermaid lives in the town which turns out to possibly be the old lady who lives in a house on a cliff with a hidden door that goes down to a beautiful logon/cave? The old lady's name is Reign. There's a big dramatic bit at the end where she is possibly exposed but I can't really remember!
