The frigid waters of the Pacific Northwest are about to get hot...

The only thing Navy underwater archaeologist Undine Gray fears more than facing former SEAL Luke Sevick is never scuba diving again. But when a dive on a Cold War-era US Navy submarine ends with an accidental explosion, she's terrified of going into the deep, forcing her to beg the most experienced diver she knows to take her back to the bottom of the cold Salish Sea.

Luke wants nothing to do with the woman who destroyed his career a dozen years ago but finds it impossible to turn his back on her plea. Caught off guard by an attraction he doesn't want to feel, he's eager to be done with this mission of mercy. But when they dive on the wreck, he only gets sucked in deeper. Someone has been digging on the Navy sub...and it appears the explosion that almost killed Undine was no accident.

To find the truth, Undine must navigate murky waters and the unexpectedly hot undercurrents swirling between her and Luke. Worse, divers are searching for something lost in US waters during the Cold War, and they'll do anything to keep Luke and Undine from finding it first.