In Book III, who killed Agamemnon and how was that murder avenged?

In Book III of the Odyssey, Odysseus' son Telemachus
arrives at Pylos to find out more information about his father Odysseus, who has been
missing for twenty years, since the Trojan War. From Nestor, the ruler of Pylos, they do
learn some things about Odysseus, but are directed to go to Sparta for more
information. 

Nestor also tells them about the ill-fated
homecoming of Agamemnon, the commander of the Greeks during the Trojan War. Agamemnon is
the king of Mycenae. While Agamemnon was gone, his wife Clytemnestra was plotting to get
rid of him. Clytemnestra is a cunning and ambitious woman who hates Agamemnon.
(Backstory: Before the war, the Greek expedition couldn't leave an island because of bad
winds caused by the goddess Artemis. In order to appease her, Agamemnon ordered that
they sacrifice a virgin girl. This virgin girl just happened to be his own daughter,
Iphigenia. They lied to her that she was about to marry Achilles, and then slit her
throat. Clytemnestra, of course, will never forgive Agamemnon for killing their
daughter.) 

Clytemnestra has an affair with Agamemnon's
cousin Aegisthus. When Agamemnon returns from the war, Clytemnestra insists that he go
take a luxurious bath. Then, Aegisthus kills Agamemnon while Clytemnestra kills
Cassandra, a Trojan princess that Agamemnon had stolen back with
him. 

This murder was avenged by Agamemnon and
Clytemnestra's son Orestes, who is furious with his mother for killing his father.
Orestes eventually kills Clytemnestra and Aegisthus. Fun family,
huh?