The Vanishing Deep by Astrid Scholte
Two sisters. One dangerous secret. Twenty-four hours to uncover the truth. Seventeen-year-old Tempest was born into a world of water. The most skilled diver on the Equinox Reef, she searches drowned cities with her older sister Elysea, seeking out old world treasures to trade for Notes.
After Elysea mysteriously drowns, Tempest scavenges the ruins alone, driven to collect enough Notes to buy her sister’s life for 24 hours, and to finally learn the secret she had kept until her last breath. However, once revived, Elysea convinces Tempest to break her out of the Palindromena research facility and they embark on a dangerous journey to discover the truth about their parents’ death.
But they’re pursued by two Palindromena employees desperate to find them before Elysea’s time is up, and to prevent them from uncovering the secrets behind the revival process and the true cost of restored lives. Dead or living, everyone must pay the price.