A vacation to the historic city of St. Augustine, Florida, quickly turns deadly for brothers Jon and Michael Rickner as an antiquities dealer is brutally murdered in his shop just minutes after meeting with them. Moments later, Jon and Michael discover an original Edison wax cylinder recording in the wreckage of the shop, one detailing the first step of an audacious treasure hunt devised by 19th-century railroad magnate Henry Flagler to lure rich tourists to his Florida resorts.

But the hunt, abandoned by Flagler on the eve of its announcement, is not as straightforward as it seems. For the tycoon's innovative attraction is tied to a priceless relic hidden by 16th-century Conquistadors and paid for in blood.

The Rickner brothers are not alone in their quest for Flagler's prize. Caeden Monk – an infamous treasure hunter exiled from the archaeological community for his destructive methods – and his devious assistant are also on the trail, and they will stop at nothing to claim the prize for themselves.

Diving headlong into a breakneck pursuit of the truth, Jon and Michael must outwit Monk, discover the secret behind Flagler's abandoned treasure hunt, and unravel a deadly riddle hidden for centuries in the very foundations of America's oldest city before an unfathomable treasure is lost forever.