Originally from Hawaii and of Polynesian descent, Kai 'Mace' Mason was originally a professional surfer and the professional snowboarder prior to losing his sister in horrific circumstances. He then left his his athletic career behind to join a covert organization where he was trained in some sort of black ops. While there, he met Luke Stark, who later recommended him to Lee Nightingale when the latter started up Nightingale Investigations. He's moody and broody. Eventually, eventually opens his own security business in LA.
- "Tall, taller even than Lee , black hair, fantastic body, jade eyes. He looked like he had a hint of Asian in him. He was beautiful. Beyond beautiful, artists and sculptors would likely beat each other to death for the opportunity to use him as a model. Not that this guy would ever model." - Ashley, Kristen (2011-03-04). Rock Chick (Kindle Locations 8560-8562).
- "Mace had to be six foot three, had the prerequisite Nightingale Investigation Team killer bod, black hair, jade eyes and a jaw so square, it could be used in math class. Indy reported that Mace had some native Hawaiian in him and was supposedly a top-notch surfer. This wasn’t surprising. Even for a big guy, Mace had the grace of a top-notch athlete who knew how to use his body. He gave up the surfing game when he discovered snowboarding. Then he lost the boarder zen when some shit hit with his sister and he gave up that game to go recreational in his spare time. Now, in his not so spare time, he hunted people for Lee and cracked heads together when the mood struck (which was a lot)." - Ashley, Kristen (2011-03-04). Rock Chick Rescue (Kindle Locations 7814-7819).
- "the tallest, hottest, coolest, most amazing guy I’d ever met. Mace with the jade green eyes. Mace with the thick, dark hair. Mace with the fantastic bod. Mace with the strong, masculine, long-fingered hands that could run so light across your skin you could almost hear them whisper." - Ashley, Kristen (2011-11-13). Rock Chick Reckoning (Kindle Locations 142-144).
- Significant Other: Stella Gunn
- Child: Tallulah Mason
- Parents: Preston Mason and Lana Mason
- Sister: Caitlin Mason
His main story is told in Rock Chick Reckoning, but he also appears in all the Rock Chick Series books and Law Man. He is also mentioned briefly in the epilogue of Hold On as standing up with Adriana Rivera at No Haines' Vegas wedding with Stella Gunn standing with No.