Bhishma Parva opens the eighteen-day war at Kurukshetra with the aged Bhishma, the Kuru dynasty's revered grand-uncle, commanding the Kaurava forces despite his deep personal affection for the Pandavas he helped raise, bound by an earlier vow of absolute loyalty to whoever occupies the throne. Before the armies clash, Arjuna, seeing friends, teachers and family arrayed on both sides, collapses in grief and moral paralysis and refuses to fight, setting the stage for Krishna, serving as his charioteer, to deliver the extended teaching known as the Bhagavad Gita, arguing across eighteen chapters that Arjuna must act according to his warrior duty while cultivating inner detachment from the results of that action, and revealing, in the poem's climactic vision, his own identity as the supreme divine reality underlying the entire universe.
Once the fighting resumes, Bhishma proves devastatingly effective, and the parva narrates the mounting Pandava losses under his command until Krishna guides the strategy that finally brings him down, placing the transgender warrior Shikhandi, whom Bhishma has vowed never to strike, in front of Arjuna so that Arjuna can fire the fatal arrows while Bhishma withholds his own attack, felling him onto a bed of arrows where, by his own choice of the moment of his death, he will linger for weeks before finally dying.