In this chapter, a Levite's concubine is raped by Benjamites of Gibeah.
This is another story of how things went "when there was no king in Israel". As with the stories about Micah, this is a key phrase to us indicating that this is a story about the anarchy that existed before a centralized authority came in to bring law and order to Israelite society.
This story begins with the concubine was in some way unfaithful to him. I don't know if that implies adultery or what. I've looked at a couple different translations, and they use phrases like "was unfaithful to him", "quarreled with him", "was untrue to him". The NASB is the most explicit, saying that she "played the harlot", suggesting that she possibly engaged in prostitution.
Either way, the man goes to collect his concubine from her father's house, and he doesn't seem to be holding her behavior against her. When he's there, there is an interesting anecdote about how the woman's father seems to be trying to delay him from leaving. To paraphrase, he says in the morning, "it's too early, have some breakfast and stay a while," and in the evening, he says "it's too late, you should rest here and leave in the morning." I don't exactly know why the woman's father was trying to delay him, maybe he wanted to keep his daughter around longer, or maybe it was a demonstration of hospitality. Something like that.
Eventually they leave, and start to go back north from Judah towards the land of Ephraim. They spend the night in Gibeah, which is in Benjamin. To remind my readers, Benjamin's inheritance was placed inbetween Judah (in the south) and Ephraim (in the north). When he gets there, he begins to camp in the town square before an old man comes by and agrees to lodge him in the old man's house. (P.S. I apologize for the ambiguous pronouns, but we aren't actually told the names of any person in this entire story.) The old man was himself an Ephraimite, so he was not a native to the town of Gibeah where they were staying.
Towards evening, a bunch of "worthless fellows" come and demand to rape the visiting man, when the old man offers both his daughter and the man's concubine to suffer their abuses. More than anything else, this reminds me of Lot offering his two daughters to the men of Sodom when the two angels visit his house in Genesis 19. It's even similar in how the old man is himself a visitor to the town and not a native Benjamite, just as Lot was a foreigner to the town of Sodom.
The big difference is that in this story, there is no angel to save the man's concubine, so when she is brought out the men rape her all night. She stumbles to the doorstep and dies there. The men, heroic as they are, soundly sleep until full daylight, and only know her fate when they go out in the morning and see her lying on the ground. Probably the worst verse in this entire chapter is verse 28, when the man looks down on his concubine and says "get up, let's go." After suffering a night of atrocities and literally dead on the ground, and this man who came to get her has no compassion whatsoever. I am utterly disgusted by his behavior in this chapter, just like I was disgusted by Lot in Gen 19. Unlike the story of Lot, in this case the abusers are themselves Israelites, men of Benjamin. In Gen 19, the men of Sodom were destroyed by fire from heaven. In this chapter, the Levite cuts up his concubine into pieces and sends those pieces into all the tribes of Israel, in order to rile up the anger of Israel against the men of Gibeah who did this.
The story continues in the next chapter, but I wonder if this chapter is meant to recall Lot and Sodom. It shows us the depth that Israel is sinking into, as they progress from theft and idolatry (in the last story) to rape and murder (in this story). Unless something changes, Israel is heading towards God's wrath and destruction like how Sodom was destroyed.