Red Letter Days Series by Rachel Caine

Jasmine "Jazz" Callender is on the downhill slide to ruin. Once a decorated homicide detective, she's lost it all: her former partner's been convicted of murder, she's been cashiered out, and she's drinking away what little self-respect she's got left. But Jazz has a talent for trouble, and somebody knows it. When a mysterious, sexy stranger comes looking for her with a fateful red envelope in his hand, she's about to make the deal of her life...for good or bad... moreJasmine "Jazz" Callender is on the downhill slide to ruin. Once a decorated homicide detective, she's lost it all: her former partner's been convicted of murder, she's been cashiered out, and she's drinking away what little self-respect she's got left. But Jazz has a talent for trouble, and somebody knows it. When a mysterious, sexy stranger comes looking for her with a fateful red envelope in his hand, she's about to make the deal of her life...for good or bad. The deal requires her to enter into a partnership with a stranger and investigate cases that arrive in special red envelopes...which is odd enough, but gets weirder as she and her new partner Lucia realize that they may be working for someone with supernatural abilities. And maybe they're not on the side of the angels anymore. less

The money Lucia and her new partner received to open their detective agency had come with strings: any assignment delivered via red envelope had to be top priority. No sweat. No one could make Lucia do something she didn't believe in -- right? Wrong. Lucia soon learned that every choice she made meant life or death for innocent people. No one could be trusted, not even the ex-cop she'd hired -- and fallen for... moreThe money Lucia and her new partner received to open their detective agency had come with strings: any assignment delivered via red envelope had to be top priority. No sweat. No one could make Lucia do something she didn't believe in -- right? Wrong. Lucia soon learned that every choice she made meant life or death for innocent people. No one could be trusted, not even the ex-cop she'd hired -- and fallen for. In fact, Ben might be her fatal weakness, if the powers warring to control the future used him to control Lucia.... less