Redux (The Variant Series, Book 3) by Jena Leigh
Alex Parker sits at the crossroads, out of time and out of place. She went back to fix the past, not to imperil the future. Rescued from the icy waters of the Bering Sea by one familiar face, she's helpless to find another. Declan O'Connell jumped with her, but where did he go?
In the middle of her search, a new threat confronts Alex. A serial killer with a taste for Variants has Seattle on edge. When she crosses the path of this vicious murderer, the revelations Alex discovers could change everything. That outcome is an unknown, but there is a terrible certainty on the table -- an impossible decision with irreversible consequences. But can Alex make that choice and commit herself and those she loves to a total Redux?