The Immortal City (The Magicians of Venice, #1) by Amy Kuivalainen

In the heart of Venice, a woman is sacrificed to a forgotten god, sparking a mystery lost for thousands of years.

Dr. Penelope Bryne is ridiculed by the academic community for her quest to find the remnants of Atlantis, but when an ancient and mysterious script is found at a murder site, she flies to Venice determined to help the police before the killer strikes again.

Penelope has spent her entire life trying to ignore the unexplainable and magical history of Atlantis, but when she meets the enigmatic Alexis Donato, everything she believes will be challenged. Little does she know, Alexis has spent the last three years doing his best to sabotage Penelope's career so doesn't learn the truth—Atlantis had seven magicians who survived, and who he has a duty to protect.

As Alexis draws her into the darkly, seductive world of magic and history, Penelope will have to use her heart as well as her head if she is to find the answers she seeks.

With the new MOSE system due to come online, and Carnivale exploding around them, Penelope and Alexis will have to work together to stop the killer and prevent dark magic from pulling Venice into the sea.