The Amtrak Wars: Bk. 3: Iron Master by Patrick Tilley
The visionary chronicle of the ultimate struggle to rule Earth continues. The year is now 2990 AD. the centuries old conflict between the high-tech, underground world of the Trackers and the primitive, surface-dwelling Mutes continues with unabaited ferocity. Steve Brickman, a Tracker wingman whose heart and mind is torn between the two cultures, embarks on his most dangerous mission to date - the rescue of Cadillac and Clearwater, two gifted Plainfolk Mutes held captive by the mysterious Iron Masters. It is a nightmare journey into the unknown but, once again, a shadowy prescence guides Steve's footsteps and endows him with superhuman speed and strength in moments of mortal danger.