When commercial diver Jilly Hale hauls up a rusted Wells Fargo safe from the depths of the Sacramento River, she hopes for a treasure to turn her life around. Instead, she finds a crude gold rush map to a legendary lost mine. Her discovery ignites more than dreams—it unleashes a killer’s fervor for keeping the mine's real secrets buried.

As the body count rises, rookie homicide detective Steve Nguyen races to connect the dots between the mine and a string of cold-case murders. But Jilly isn't waiting to be rescued. Armed with grit and a map, which could cost her everything, she's ready to dive headfirst into danger-because this time, the treasure isn't just gold, it's survival.