From the moment they find an unusual shell on the beach, the twins' peaceful holiday with their grandparents turns into a spine-tingling, fast-moving adventure.
When their new friend, Sandy, goes missing in mysterious circumstances, Mia experiences visions that lead her to believe that she has been kidnapped and is in danger. She shares her fears with Ellie and Lucy, and they agree to go with her in search of their friend. Now Mia must draw on every ounce of her witchery if they are to outwit the kidnappers, find Sandy, and save her from further harm. Can they do it? Mia might be a sea witch, but she is very young and inexperienced and still getting the hang of spells. But the clock is ticking ...