With Your Shield. Four Horsemen Tales, #10

Staff Sergeant Markus 'Spartan' Nicolos is one of the Intelligence Department's best. A hacker who can beat any code, he's in charge of communications intercepts for the Golden Horde's Computer Operations section. When people can't break a code, they bring in Spartan. It wasn't always this way, though. Spartan used to be a frontline CASPer pilot-someone who could be counted on to get the job done and bring the squad home safely.until he lost his entire squad in an ambush.
He also lost his edge in the attack, and he swore he would never pilot a CASPer in combat again. Everything changed, though, when he came up with an idea for a new type of scout CASPer-one that would prevent what happened to him from ever happening again. He's been given a mech to convert and a team to help him bring his idea to reality. And he's been given a chance to test it out on a Golden Horde deployment. But in the time immediately before the events of the Omega War, forces are already moving behind the scenes, and nothing is as it seems.and they're bringing along Spartan's combat mech-which he said he'd never pilot in combat again-just in case.