Deep in the Australian wilderness, a famed sinkhole renowned as a stunning freediving spot attracts people from all over the world.

But there's a dark, puzzling mystery when a local sports hero - and the glamorous face of a high-adrenaline video channel - is found dead far beneath the surface. Despite diving the sinkhole hundreds of times, his lifeless body is discovered dressed in normal clothes, handcuffed to a supply line. With no witnesses - and evidence submerged 30 metres underwater - how can Detective Dana Russo unravel such a shocking case?