The climactic fight between the Enterprise and Khan's Reliant.
Khan Noonien Singh, marooned for years on Ceti Alpha V after Kirk's decision to exile him, escaped and seized the USS Reliant. He was driven by revenge and by his hunger to obtain the Genesis Device, a technology that could transform lifeless worlds into living ones or serve as a terrible weapon.
Khan hunted Kirk across space, wounding the Enterprise in an early ambush before the two ships met again in the Mutara Nebula. Inside the cloud, shields and sensors failed, and the fight became a duel between old adversaries decided by cunning rather than firepower. Kirk used Khan's unfamiliarity with three-dimensional tactics against him and crippled the Reliant.
Khan, dying, triggered the Genesis Device, and the Enterprise was trapped in the blast zone with a damaged warp drive. Spock entered a radiation-filled engine compartment to restore power and saved the ship, dying as a result. Genesis then formed a new planet from the nebula's matter. Kirk, McCoy, Saavik and David Marcus faced the cost of Spock's sacrifice and the weight of what they had witnessed.