Thanks in advance to anyone who might know, as it's driving me mad.
It's a modern novel, probably last 20 years or so, and set, I think, in the Highlands or Islands of Scotland. There's a female protagonist. She's new to the area. At one point she climbs into a ruined church. There's another family she meets, and they have a young teenager son. He goes missing and assumed drowned, but his mother confides that in fact they were only his 'keepers' and he was a mythical creature (selkie?) and has returned to seal form.
It is NOT Night Waking by Sarah Moss, I thought it was but I've just read that and it wasn't.
If anyone can get this from my vague description I would be most grateful!