Tribulation (Soulless Wanderers, #0)

Before the apocalypse, Daniel was just your average, run-of-the-mill serial killer.
Daniel is learning that being a serial killer is hard work. Luckily, he has one friend in life that is just like him, but far more experienced. Greg is more than happy to teach Daniel everything he knows about killing and not getting caught. But when a mysterious woman shows up, she takes Daniel on a reckless ride of passion and killing, making him question everything Greg has taught him.