As Jack and Joan prepare for her first southern hemisphere Christmas by the beach, a reef dive goes catastrophically wrong, and Joan does all she can to save an injured diver. With a young woman's life in the balance, Joan and Jack discover the accident is really a case of sabotage. The mystery hits home for Jack, who secretly seeks out a woman from his past to make amends for his mistakes.

Rebecca's sudden arrival throws Joan into turmoil as she struggles with how to tell her daughter about the murder charges against Ian. Tracing Ian's last movements is put on hold when a neurodivergent Indigenous boy goes missing and the search becomes a potential abduction investigation. Rebecca is determined to bring her mother back to London and begins to question Joan's well-being.