MechWarrior 4: Black Knight follows Eric McClair, a recently discharged Mech pilot who once served House Davion. Looking for steady work, he joins the Black Knight Legion — a mercenary unit led by the experienced Colonel Lawhorn. Early contracts are routine: escort duties and support work for the Corvatti Corporation. Then Major Clarrisa Dupree, a Lyran Alliance liaison officer, arrives with something more significant — a contract to help retake Kentares IV on behalf of House Steiner, sweetened with a gift of fresh Mechs. The Legion deploys and begins running disruption operations against the forces of Duke Ian Dressari.
The arrangement does not hold. Dupree reveals her true allegiance — she has sided with Dressari — and launches a coordinated attack on the Legion. Colonel Lawhorn is killed in the ambush, and command falls to McClair. Rather than withdraw, he presses forward on the original objective, working with local resistance fighters to fight his way to Dressari's palace. The campaign ends there, with McClair confronting and killing Dressari along with his inner circle.
The score with Dupree remains. McClair tracks her to the planet Voltrat III, where the Black Knight Legion destroys her and every Lyran Mech she commands. With the fight over, McClair claims Voltrat III as the Legion's permanent new home.