Atreus and Thyestes
Atreus and Thyestes were brothers, the sons of Pelops and Hippodameia. The brothers grew up together and played together. But instead of loving each other, they were always rivals in everything. This may have been partly because of the curses on Tantalus, their grandfather, and Pelops, their father.
One day, Atreus promised to sacrifice the best lamb in his flock to the goddess Artemis. Later that afternoon, as he went walking among his sheep, Atreus found a lamb with a golden fleece! Certainly he should have sacrificed that one to Artemis, but he didn't want to sacrifice such a beautiful thing, so he killed the lamb and kept the golden lambskin in a box instead.
But Atreus' wife, the Queen, was secretly in love with Thyestes. She agreed to steal the golden lambskin and give it to Thyestes. Then Thyestes dared Atreus to make a deal with him. He said, "Let's say whoever has the golden sheepskin can be King of Mycenae." Well Atreus knew that he had it in his box, so he agreed. But then it turned out that Thyestes had it, so he got to be King. Atreus was very angry.
Atreus went to Zeus (his great-grandfather through Tantalus) and complained. Zeus told Atreus to make a bet with Thyestes that if the sun ran backward, Atreus could be king again. Thyestes thought, "Nobody can make the sun run backward!" so he agreed. But the gods can do anything, so Zeus did make the sun run backwards. Atreus got to be King of Mycenae again, and he banished Thyestes from the kingdom.
But when the slave took the cover off the dish, Thyestes was horrified to see his two sons' bloody heads and hands and feet! Atreus had murdered them and cooked them and served them to him for dinner. Thyestes just ran out of the palace and never came back again. He did, however, have one more son, Aegisthus, who eventually avenged his dead brothers.
Learn by doing: check out a lambskin in a store or on a lamb
More about Atreus' son Agamemnon
The Pride of Lions: The Story of the House of Atreus, by Norma Johnston (2002, unfortunately out of print right now, but maybe your library can find it). For teens.
The Oresteia, by Aeschylus, translated by Robert Fagles (Penguin Classics). The story of Atreus' son Agamemnon and grandson Orestes. Fagles is a great translator! Includes a version for performance.
Aeschylus, by John Herington (1986). A discussion by a specialist about the life of Aeschylus and why his plays are written the way they are.