The book falls in two halves. The first seven chapters are the threat: a great king sends his general Holofernes west with an enormous army to punish the nations that refused him troops, and city after city surrenders. Only the Jews, lately returned from exile and with the Temple restored, refuse, and fortify the passes. Holofernes asks who they are; the Ammonite Achior tells him the truth, that this people cannot be beaten unless they sin against their God, and is tied up outside the town of Bethulia for saying it. The siege takes the springs, and after thirty-four days the elders agree to surrender in five days if God has not acted.
Judith appears only then, in chapter eight, and immediately rebukes the elders for setting God a deadline. She prays, takes off her widow's clothes, dresses to be looked at, and walks out with a maid and a bag of her own permitted food. In the camp she flatters Holofernes with a prophecy that his victory is assured because the Jews are about to break their law, establishes a nightly habit of leaving the camp to pray, and on the fourth night, alone with him in his tent after a banquet at which he has drunk more than on any day of his life, takes down his own sword and beheads him with two strokes.
She walks out past the guards as usual and is back in Bethulia before dawn with the head. Achior, shown it, converts and is circumcised. The Israelites sortie at first light, the Assyrians find their commander decapitated and rout, and Judith sings a victory hymn, refuses every offer of marriage, frees her maid and dies at 105.