Shadow Zone: Hannah Bryson series #2

The second book in the Hannah Bryson series. The story revolves around Hannah Bryson, a submersible designer, who discovers the truth about the mysterious demise of the ancient underwater city of Marinth in the Atlantic Ocean.
Hannah's findings reveal that Marinth's explosive secret could have dire consequences for the modern world. When her key artifact is hijacked, she must race against time and a dangerous enemy to prevent a global catastrophe. Along the way, she teams up with Kirov, a mysterious and deadly man from her past.
It's a heart-pounding adventure filled with suspense, action, and intrigue.