The Numbers Killer by Jenifer Ruff

You’ll never view odd numbers the same way again.

When a key witness in an organized crime trial turns up dead in his kitchen with liar and the number two scrawled on his forehead, the FBI assumes the murder was a hit to silence him. Then the calls start coming in—more victims with similar markings and no connection to the mob.

As agents Victoria Heslin and Dante Rivera struggle to catch a break in the case, they receive a series of cryptic, personal messages from the killer, complicating the investigation. Something disturbing and frightening is underway, and anyone might be next, including the agents, unless they uncover the common denominator.

The Numbers Killer is the first book in the Agent Victoria Heslin Series and can be read as a standalone.