Detective Sergeant Mark Ariti has taken a few days’ holiday in Broken Bay at precisely the wrong time. The small fishing town on South Australia’s Limestone Coast is now the scene of a terrible tragedy. Renowned cave-diver Mya Rennik has drowned while exploring a sinkhole on the land of wealthy farmer Frank Doyle. As the press descends, Mark’s boss orders him to stay put and assist the police operation. But when they retrieve Mya's body, a whole new mystery is opened up around the disappearance of a young local woman 20 years before. Suddenly, Mark is diving deep into the town’s history – and in particular the simmering rivalry between its two most prominent families, the Doyles and Sinclairs. Then Cherie Swinson, a former actress, is murdered in the Sinclairs's old home – and Mark is left wondering which is more dangerous: Broken Bay’s hidden subterranean world or the secretive town above it.