First up, Antinoös. Odysseus him with an arrow to the throat while he's drinking wine.
It's justice time.
Realizing that their weapons are gone, the suitors scatter.
Eurymachos begs for Odysseus to have mercy on the rest of the suitors, now that he's killed the worst of them (that would be Antinoös).
So, Eurymachos tries to rally the suitors to fight Odysseus, who responds by promptly killing Eurymachos with an arrow to the heart.
As Amphinomos rushes Odysseus, Telemachos stops him with a spear to the heart.
Telemachos then runs to the storage room, grabbing more weapons, and arming the four allies (Odysseus, himself, Eumaios, and Philoitios).
Melanthios sees Telemachos go to the storage room and quickly does the same in order to arm the suitors.
Odysseus is none too happy to see that the suitors suddenly have weapons.
Telemachos knows it's his fault for leaving the storage room door open and confesses it to Odysseus, who orders the two herdsmen to follow Melanthios, tie him up, and lock him in the storage room so he can do no more harm. They obey.
All right, guys, less apologizing/ordering and more fighting! Especially since the suitors now have Odysseus and Co. cornered and incredibly outnumbered.
Athene arrives, disguised as Mentor. Odysseus recognizes her for who she is and calls help.
The suitors beg Mentor/Athene not to help Odysseus, threatening him with death if he does.
She turns to Odysseus and tells him to show the suitors his stuff (i.e., the skills he used against Troy)—justice, she says, is on the way.
But she holds back. Odysseus and Telemachos have yet to prove themselves worthy of her assistance. She watches her two little pet mortals from the roof and passively protects them while they pick off suitors one by one.
At last, Athene's sign—the aegis or "great shield"—shines in the air in the hall and the suitors realize that Odysseus has godly help. They panic. Some beg for mercy, but Odysseus is ruthless.
So ruthless, in fact, that he spares only Phemios the singer and Medon the town crier, because Telemachos swears they're loyal.
Finally, all the suitors are dead. Bloodbath? Check. Revenge? Check. Mischief managed? Check.
Odysseus calls for Eurykleia to bring all the unfaithful maids to him.
Eurykleia is all, "Um, how 'bout putting on some non-bloodbath clothes first?", and Odysseus is all, "No."
Of the fifty maids in the household, twelve have proved disloyal. Odysseus forces them to drag the corpses of the suitors outside and clean the hall.
He orders his son to then hack the disgraceful women to pieces outside, but Telemachos thinks this is too noble a death for these "sluts." Instead, he hangs them, which is apparently worse than being hacked to pieces.
Then the good guys torture and kill Melanthios.
Odysseus orders Eurykleia to bring brimstone, a brazier, and medicinal herbs so he can purify the great hall.
We're thinking some bleach and a mop would be a good idea, too.
Apparently, so does Eurykleia, since she tries to get him to clean up first. He refuses.
Odysseus purifies the hall, and all the maids and servants who remain with many hugs and tears (and grimaces, because as far as we can tell, he's still wearing his bloody clothes).