From publisher blurb:
SUNKEN SARCOPHAGUS has the player characters delve deep into a lagoon known as Witch’s Hole. The mission is to find a sunken sarcophagus that holds the fabled artifact THE BLACK IMP. This artifact is a highly-valued item coveted by a wealthy art and relics collector eager to use its powers before the idol is used by the forces of evil Deep Ones located in their underwater castle keep. Can the PCs cut past hordes of sharks, Deep Ones, giant electric eels, and a Deep One Shaman to find this powerful relic? Not if The Sleeping Mother can help it. And even if the PCs do manage to seize this prize, what foul creature of the deep is waiting for them at the very end to serve as a tasty, tentacled grand finale.
Most of THE BOOK OF DARK SECRETS short adventures have a darker than the norm undertone to them, hence the series title name. This is not a particularly dark adventure, but still, as always, this is for adult and mature audiences, please.