The Treasures of Venice by Loucinda McGary

Samantha Lewis is in Venice, taking a tour by herself that was supposed to have been her honeymoon. When she is approached by a handsome stranger who pretends to be meeting her at a cafe, she decides to play along. His name is Kiernan Fitzgerald, and he is definitely more than he seems. Sam is instantly drawn to him, but she feels crazy for getting so attached after just an hour or two. When he reappears in her hotel room later that night, injured and needing her help, she is immediately drawn into his troubles.
Kiernan is looking for the Jewels of the Madonna. His sister was also searching for the Jewels, until she was kidnapped. Now the only way for Kiernan to save her is to find them himself and turn them over to the kidnappers. He doesn't want to get anyone else involved, but he can't seem to stay away from Sam. They are drawn to each other in a way neither can explain, and so they stop trying to fight it, and start trying to save Kiernan's sister, before it's too late.
Besides being a story told in the present time, The Treasures of Venice is also told in flashbacks to fifteenth century Venice, where the reader learns the story behind the Jewels that Kiernan seeks. The lovers in that story have some striking similarities to Kiernan and Sam - coincidence? As Sam and Kiernan get closer to the Jewels, and to each other, they both begin to wonder if they have some sort of deeper connection that goes beyond the present time. This element of past lives adds another dimension to the story and the mystery, making for a more interesting read. I liked the parallels between the two stories. This is an exciting, romantic adventure book that any readers of romance will enjoy.