Asaro, Catherine. Saga of the Skolian Empire.

"Major Bhaajan achieved the impossible. Born to the Undercity, the slums on the planet Raylicon, she broke free from crushing poverty to become a military officer with Imperial Space Command. Now retired, she walks Undercity as a private investigor. Summoned by no less than the Ruby Pharaoh herself, Bhaajan is tasked with finding a killer. The Ruby Pharaoh witnessed a Jagernaut cut down an Assembly Councilor which shouldn't have been possible. The Jagernauts are the military elite of elite soldiers with a spinal node implanted that should have prevented the murder. But the Ruby Pharaoh is sure of what she saw and has reason to believe that the Jagernaut will kill again unless Major Bhaajan can stop it"--