Songbird. The Zeta Cartel Novels, #2

Stunningly beautiful Solitaire Rotheringham is no angel. Shot and left for dead at sixteen, Solitaire does what it takes to survive. Faced with a gruesome death at the hands of Arturo Vazquez, Mexico's most feared cartel boss, she persuades him to take her on as a mistress. To her surprise, she finds love. However, life in the cartel is lethal, and Solitaire has a dangerous secret.   When cartel boss Arturo Vazquez discovers his girlfriend is a DEA rat and his deputy is staging a take-over, Arturo fixes his problems by killing everyone - except for Solitaire, his deputy's unwilling mistress.
Solitaire is intelligent, tough, and shares Arturo's interest in BDSM. Arturo falls head over heels but someone is leaking information - and the evidence points at Solitaire. Songbird is a compelling tale of vengeance, murder, cartel violence and finding love in the darkest of times. It is the second Zeta Cartel novel, and can be read as a standalone.