Choke Hold (Angel Dare Series) by Christa Faust

INSIDE THE WORLD OF MIXED MARTIAL ARTS - AND MURDER... 

Angel Dare went into Witness Protection to escape her past -- not as a porn star, but as a killer who took down the sex slavery ring that destroyed her life. But sometimes the past just won't stay buried. 

When a former co-staris gunned down, it's up to Angel to get his son, a hotheaded MMA fighter, safely through the unforgiving Arizona desert, shady Mexican bordertowns, and the seductive neon mirage of Las Vegas...