Word reaches Holofernes that the Israelites have locked their doors and thrown away the key. Rather than bashing them over the head with a rock, he asks his generals about these crazy people who won't let him take over their lands and burn all their stuff down.
So one of the generals, Achior tells him about the old testament and says they should only invade if they can find the Israelites have been sinning, because otherwise god with smite them. The other generals do not like this, and want to kill Achior right away, then invade.
Holofernes scoffs that the Israelites' god is nothing against King Nab (who, you will remember, has also declared himself god), and if Alchior likes the Israelite god so much, he might as well give him to the enemy. He assigns two of his slaves to escort Alchior to Bethulia.
The men of Bethulia see Alchior approaching and take out their weapons while the men with slingshots hold the approaching trio off. The slaves tie Alchior up and go home. The Israelites pick him up and take him back to the city, where they present him to the mayor, who calls all the citizens together to try Alchior. Alchior tells them what happened in Holofernes' tent, and the people fall all over the place to worship god. Then they have a feast for Alchior, then they pray some more.
Holofernes declares war and sets up camp in the valley under Bethulia. The Israelites see this and arm themselves. As he and his scouts try to determine the best way of attacking the city, one of his generals rides up and points out how hard it is to attack a fortified city on top of the hill. The smarter move, he points out, would be to simply cut off the city's water supply. Holofernes sees the merit of this plan and tells the army to encircle the city and wait.
The siege lasts 34 days, during which the Israelites use up every drop of water in the city, and everybody gets super thirsty. They go to the mayor and ask him to sue for peace, because it only takes them 34 days to lose all faith in god. Now they want to give Holofernes the whole city and become slaves. Then they cry, with what tears is unclear, and the mayor asks them for five more days in hopes god will remember them. They agree to wait.