A lot of people think the Iliad covers the whole Trojan War. It doesn't. It starts in the tenth year and stops before the city falls. The wooden horse isn't in it, and neither is the death of Achilles. It runs for about fifty days, and the first line tells you what it's about: the wrath of Achilles. Not Helen, not Troy. Wrath.
A plague over a girl
A priest of Apollo named Chryses comes to the Greek camp to ransom his daughter from Agamemnon, who has taken her as a prize. Agamemnon sends him away roughly. Chryses prays, and Apollo comes down "like night" and shoots plague arrows into the camp, mules and dogs first, then men. Pyres burn for nine days.
Achilles calls an assembly. A seer names the reason. Agamemnon gives the girl back but, to keep his pride, takes Briseis, who is Achilles' prize. Achilles nearly draws his sword. Athena catches him by the hair, unseen by anyone else, and he holds back. Then he walks away from the war and prays to his mother Thetis. Already you can see how the poem works: the god's anger comes from a human insult, not the other way round. A priest was disrespected, and an army pays for it.
The family on Olympus
Thetis goes to Zeus and asks him to let the Trojans win until the Greeks honor her son. Zeus agrees, even though he knows his wife will give him trouble. She does. He threatens her. And it is Hephaestus, limping around the hall with the wine jug, who breaks the tension, and all the gods roar with laughter.
The gods in this poem are a household. They bicker, they scheme, they take sides. In Book 14, Hera borrows Aphrodite's embroidered girdle and gets Sleep to help her put Zeus under on Mount Ida so the Greeks can push back. In Book 5, Diomedes wounds Aphrodite on the wrist and she flees to her mother, crying. Zeus tells her war is not her business. Diomedes also wounds Ares, who bellows and runs to his father to complain, and Zeus tells him he is the most hateful of all the gods on Olympus.
And what comes out of them when they bleed isn't blood. Homer calls it ichor, and he explains why: the gods don't eat bread or drink dark wine, and so they have none. I always liked the logic of that. You are what you eat.
The thing Zeus can't fix
In Book 16, Zeus watches his own son Sarpedon about to die. He wonders aloud whether to snatch him out of the fight. Hera answers sharply. If you do, every other god will want to save their own sons, and then where are we? Zeus gives in. He sends a rain of blood drops to honor the boy.
Could Zeus have saved him? Homer never really says. I think that is on purpose. The poem lets you feel the weight of fate without ever explaining who is holding it.
Two angers
Achilles refuses to fight until Hector kills his friend Patroclus, who has gone into battle wearing Achilles' armor. After that, the anger changes direction. It isn't aimed at Agamemnon any more. It is aimed at Hector, and Achilles kills him, chases him three times around the walls first, and then drags his body behind the chariot for days.
Then comes Book 24, which for me is the reason the poem exists. Old Priam, Hector's father, is guided by Hermes across the plain at night to Achilles' tent. He kneels and kisses the hands that killed his son. He asks Achilles to think of his own father. And Achilles does. They weep together, one for his father, one for his friend, and one for his son. Achilles gives the body back.
While they talk, Achilles tells him that Zeus keeps two jars at his door, one of evils and one of gifts. Some people get a mix. Others get only the evil. It is the kindest, bleakest thing anyone says in the whole poem, and it comes from the man who caused most of the harm.
My reading
Gods in this poem can't lose anything that matters. They can be wounded and healed by lunchtime. That is why they are funny when they argue and why the humans, who can really die, are the only ones who can be tragic. The poem ends not with a victory but with a funeral for the enemy, and with two men who have every reason to hate each other sitting down to eat. I think that is the whole point. This is our reading.