This expansion pack to "Mechwarrior 4: Vengeance", developed by Cyberlore Studios and published by Microsoft, is another title in the highly successful Mechwarrior series.

The story follows Eric McClair, a recently discharged 'Mech pilot from House Davion. Eric joins the Black Knight Legion, a mercenary group led by Colonel Lawhorn. Initially taking on mundane escort contracts from the Corvatti Corporation, the Legion is approached by Lyran Alliance mercenary liaison officer, Major Clarrisa Dupree. The major offers a contract for the Legion to assist in the retake of Kentares IV on behalf of House Steiner and gives free 'Mechs to the Legion as a gesture of goodwill. On Kentares IV, the Legion runs disruption missions, taking out key assets to Duke Ian Dressari's forces. The Legion is soon double-crossed by Major Dupree who is now in allegiance with Ian Dressari. The Legion is attacked by Steiner mechs, killing Colonel Lawhorn and putting Eric McClair in charge of the company. McClair decides to continue the original contract, going after Ian Dressari. Working with rebels, McClair works his way to Dressari's palace and kills him along with his closest supporters. McClair then sets his sights on Major Dupree. Hunting her down to the planet Voltrat III, the Legion kills Dupree and her entire garrison of Lyran 'Mechs. McClair decides to make Voltrat III the new home of the Black Knight Legion.