Do mermaids take people's lives or save them? This question has been worrying the residents of the Dark Sea for more than one year. Every time during a storm, they meet a mysterious girl on the shore with a lantern in her hands, and then with horror they see her mermaid tail flashing in the sea. Martha knows the answer to this question, because she, too, is a mermaid. The mystery of an old shipwreck, family secrets, magical pendants full of magic, and a meeting with a desperate mermaid who is ready to do anything to return what was lost are just part of what 15-year-old Marta will face in Darksea, a small seaside town lost among rocks.