II Chronicles 22, The Rise of Athaliah

The kings of Judah, after Solomon, have been Rehoboam, Abijah, Asa, Jehoshaphat, Jehoram. Jehoram's reign has been a bloody disaster (literally.) The date is now about 841 BC.

2 Chronicles 22:1-4, Ahaziah king

The people of Jerusalem made Ahaziah, Jehoram's youngest son, king in his place, since the raiders, who came with the Arabs into the camp, had killed all the older sons. So Ahaziah son of Jehoram king of Judah began to reign.

Ahaziah was twenty-two years old when he became king, and he reigned in Jerusalem one year. His mother's name was Athaliah, a granddaughter of Omri. He too walked in the ways of the house of Ahab, for his mother encouraged him in doing wrong. He did evil in the eyes of the LORD, as the house of Ahab had done, for after his father's death they became his advisers, to his undoing.
 

The evil northern kingdom of Ahab and Jezebel has an effect on the southern kingdom as the couples' daughter, Athaliah, influenced both her husband, Jehoram and her son, Ahaziah, in their idolatry. 

2 Chronicles 22: 5-6, Death of Ahaziah

He also followed their counsel when he went with Joram son of Ahab king of Israel to war against Hazael king of Aram at Ramoth Gilead. The Arameans wounded Joram; so he returned to Jezreel to recover from the wounds they had inflicted on him at Ramoth in his battle with Hazael king of Aram. Then Ahaziah son of Jehoram king of Judah went down to Jezreel to see Joram son of Ahab because he had been wounded.
 

Through Ahaziah's visit to Joram, God brought about Ahaziah's downfall. When Ahaziah arrived, he went out with Joram to meet Jehu son of Nimshi, whom the LORD had anointed to destroy the house of Ahab. While Jehu was executing judgment on the house of Ahab, he found the princes of Judah and the sons of Ahaziah's relatives, who had been attending Ahaziah, and he killed them.

Control of the town of Ramoth Gilead, east of the Jordan, has flowed back and forth between Israel and Aram-Damascus. Ahaziah, a grandson of Ahab and Jezebel, foolishly joins the northern kingdom in a campaign to retake that region and there Joram, king of the northern kingdom, is wounded. Ahaziah visits Joram after the battle, just as Jehu is overthrowing that kingdom.

Jehu (whose story is told more thoroughly in 2 Kings 9-10) overthrows Joram in Israel/Samaria and massacres the descendants of Ahab. Ahaziah is caught in the middle of that and barely escapes -- for the moment.

2 Chronicles 22: 9, Murder of Ahaziah

He then went in search of Ahaziah, and his men captured him while he was hiding in Samaria. He was brought to Jehu and put to death. They buried him, for they said, "He was a son of Jehoshaphat, who sought the LORD with all his heart." So there was no one in the house of Ahaziah powerful enough to retain the kingdom.
 

Ahaziah is caught by Jehu and murdered. but, as the son of Jehoshaphat, he is buried with respect.

2 Chronicles 22: 10-12, Athaliah and Jehosheba

When Athaliah the mother of Ahaziah saw that her son was dead, she proceeded to destroy the whole royal family of the house of Judah. But Jehosheba, the daughter of King Jehoram, took Joash son of Ahaziah and stole him away from among the royal princes who were about to be murdered and put him and his nurse in a bedroom. Because Jehosheba, the daughter of King Jehoram and wife of the priest Jehoiada, was Ahaziah's sister, she hid the child from Athaliah so she could not kill him. He remained hidden with them at the temple of God for six years while Athaliah ruled the land.

Athaliah appears to be more in league with the northern kingdom and certainly opposed to the descendants of Ahaziah. She attempts to destroy the descendants of Jehoram but a daughter of Jehoram, Jehosheba, moves quickly to protect her nephew, Joash, and hide him in a bedroom of the palace. Because Jehosheba is the wife of the high priest, Jehoiada, they are able to eventually hide Joash in the temple.

The six year reign of Athaliah is also told in 2 Kings 11.