World-famous oceanography institute RIO recently opened a new restaurant and tiki bar to give divers somewhere nearby to grab a snack and a drink. The place is a hit, and Fin and the team are basking in the glow of success. Until the morning an unknown young woman is found dead in the bar, the victim of a needle spike. DS Scott asks Fin to help with the investigation. To make matters worse, Fin's under the gun from the the sponsor of the institute's annual documentary, who threatens to revoke their contract and hire her ex's company instead if they miss the deadline. Without the money from that sponsorship, RIO will have to shut down most of its research. Fin calls in Christophe, a world champion freediver to help her get ready for the filming. And then, one of their own vanishes. Fin is convinced that the notorious oligarch Seb Lukin is behind it all. She and Newton head to Lukin's mega-yacht to see what they can uncover. It seems the missing women have vanished into thin air, but Fin will do whatever it takes to find them and bring them home. Will she succeed? Read Hidden Depths now to find out.