The Girl with a Clock for a Heart by Peter Swanson

The Girl is like the book version of a film noir. Average Joe George Foss is going about his mundane life when he suddenly spies the girl from his past that he never forgot--the alluring Liana Decter. Soon she's entangled him in a messy web involving stolen money, stolen diamonds, suspicious deaths--and several visits from the police.

A lot of the book is told in flashbacks, as George recalls his early relationship with the elusive Liana. And we see how his opinion of her and feelings toward her slowly evolve as he realizes just what she's capable of. I read almost the whole book in one sitting.