Nikolai by Lisa Marie Rice

Buried secrets. Explosive passion. One unforgettable escape.
Security consultant Nick Garin is called to the US Consulate in Naples, Italy, to investigate an intel leak. When he runs into the stunning and brilliant historian Parker Donovan, he can’t take his eyes off her. Nick insists on tagging along to Parker’s archeological excavation, but an earthquake buries them underground.

Crawling in the dark through ancient passages, they discover an ancient deadly secret.
But someone close has betrayed them. Parker and Nick are the only ones standing between weapons of mass destruction and the Mafia—and now they must fight like hell, for their lives, and their love…