Bagoas shuts the party down, leaving Judith and Holofernes alone inside. Holofernes is passed out drunk. Judith asks her slave girl to stand outside her room and wait for her so she can go and pray. On the way out, she stops in on Holofernes. As she looks at him, she prays silently to god to take advantage of this situation. She finds a big knife hanging from one of his bedposts, grabs his hair, begs god for strength, and cuts of his head with two grisly blows. She hands it to her maid, who puts it into the sack of meat she's already holding. Somehow they pass through the camp as though they're going to prayer, and no one notices that they're presumably covered in blood, because cutting off heads is messy. Anyway, no one disturbs them and they go back to Bethulia.
As she approaches the gates, she calls out to the gatekeeper to open up. The men of the city hear her and come running. She brags to them that god used her hands to destroy their enemies and holds up the head in triumph, adding that as a hot chick, no one was expecting her. This would still be the case today. Far from being disgusted, the elders praise her.
Judith wants the head on a spike. Then she wants the Israelites to suit of armor up and head down to the Assyrian camp. The Assyrians will be shocked and will go to find Holofernes. Finding him sans tête, they will flee. The Israelites will then pursue them to the sea coast, killing them on the way.
Before any of that, though, she wants to see Achior the Ammonite to show him her prize. He's shocked, but also praises Judith and wants to hear the story in gory detail. She tells him, and the people start shouting for joy. Right then and there, Achior circumcises himself, and is accepted as a new Jew.
In the morning, they put Holofernes' head on a spike and go down to confront the Assyrians. Somehow, Bagoas is able to knock on Holofernes' door, even though he's in a tent. He's also able to open said door, only to find Holofernes, but not his head. He goes to Judith's tent and discovers it devoid of any heads. He jumps up to explain to the soldiers that they got played by a hot chick, and they're all completely shocked.