A long, boring play by Euripides about how Agamemnon sacrificed his daughter in order to speed the Greek fleet to Troy.
Essentially, the plotline is this: Agamemnon is chief of the Greek Fleet. Unfortunately, there's no wind, so the fleet isn't going anywhere real fast. This isn't good for Mr. Commander-in-Chief's ambitions. Luckily for Agamemnon, there is a solution. Unluckily for his daughter, it involves sacrificing her to Aphrodite.
In order to get her down to Aulis for sacrficing, he invents a story about marrying her to Achilles. The idea is that if Clytemnestra (his wife) thinks that her daughter will be glordiously wed to Achilles (Mr. Big Hero), she'll be all too happy to send Iphigenia down to Aulis.
Of course, she'll be very disappointed with the death of her daughter, but nothing that ten years won't fix.
Agamemnon's plans look to be in jeopardy, though, when Clytemnestra tells him of the Wedding-- Which he, of course, hadn't heard anyhting about. Clytemnestra is rightly intrigued, and makes inquiries, with an old servant of Agamemnon. The plan is revealed to her, so she shares the knowledge with Achilles. Achilles is none-too-pleased, as he now wants to marry Iphigenia.
Iphigenia and her baby-brother supplicate Agamemnon to spare her. He's in quite a bind, now-- The entire army is out for her blood. Her death is the only way to get things moving. Achilles, the archtypical hero, offers to protect Iphigenia, even at the risk of being stoned to death by the army.
Fortunately for everyone involved, Iphigenia figures that her death will bring great honour to Greece. She thinks that it's unfair that no one should question the inevitable deaths of many greek soldiers, when such a fuss is made over her. She volunteers to be sacrificed. She is. The End.