Children search for missing (pearls?) from necklace on beach to save mermaids. I would have read this in the early 70s to 80s, and it very likely could have been a 2nd hand book. Some children are searching on a beach for the missing (I think pearls) from a necklace. The necklace needs to be complete to save (possibly) mermaids from something. I remember rockpools being involved. This has been bugging me for years, and I’d be so grateful if someone could solve it for me.