The Venetian Key - Adrian West Adventures, #4

An earth-shattering secret. A long-lost key. A lethal pursuit... After a cryptic letter summons Adrian West and Nick Harper to Venice, a revelation from the past shatters Adrian's world... They must pick up the pieces to follow a trail of cryptic clues, unraveling the threads of a conspiracy rooted deep in Venetian history. In a desperate race from the canals of Venice, the ancient streets of Dubrovnik, to the Byzantine-era relics of Istanbul, Adrian and Nick must prevent a clandestine society from carrying out a lethal, centuries-old agenda that could spell humanity's extinction...
For fans of James Rollins and Dan Brown, start reading this fast-paced thriller now!