The frame is doubled. Ugrashravas recites the epic to sages in the Naimisha forest, having heard it recited by Vaishampayana at the snake sacrifice of King Janamejaya, Arjuna's great-grandson, so the story arrives as a report of a report, and the audience inside the text are the descendants of the people in it.
The narrative core is family. Five Pandava brothers and a hundred Kaurava cousins contend for the Kuru throne; Draupadi is won by Arjuna and married to all five; Yudhishthira gambles away kingdom, brothers, himself and Draupadi in a rigged dice game, and her humiliation in the assembly hall becomes the injury the war exists to answer. Thirteen years of exile follow, then the failure of every attempt at settlement, then eighteen days of fighting at Kurukshetra in which the Pandavas win by a series of deceptions and almost everyone dies.
But the battle books are a fraction of the whole. The Shanti and Anushasana Parvans, delivered by the dying Bhishma from a bed of arrows, run to some 20,000 verses of instruction on kingship, law, caste, penance and liberation, and constitute one of the largest bodies of political and ethical thought in Sanskrit. Embedded stories, Nala and Damayanti, Savitri who argues Death out of her husband, Shakuntala, the abridged Ramayana, were extracted and retold for centuries. The Bhagavad Gita sits in the sixth book, spoken before the fighting starts. The Harivamsa, a genealogy of Vishnu and an account of Krishna's youth, is appended as a supplement.
The text's own boast is that whatever is here on dharma and the rest may be found elsewhere, and what is not here is nowhere. It is close to true of its contents and exactly true of its ambition.