II Kings - Chapter 10
And that's the story of Ahab...
Jezebel may have been the queen, but Ahab had other wives and concubines. Through them, he had 70 sons and grandsons, most of whom were in Samaria. Yehu wrote to the governors of Jezreel and Samaria asking if they were going to support him or try to prop up one of Ahab's descendants as a successor. Seeing that Yehu had defeated both Yehoram and Achaziah, the elders of the cities decided not to oppose him. Yehu said, "If so, you must send me the heads of Ahab's heirs." Having no alternative, the elders complied. Yehu had the heads placed in two piles by the gates. He addressed the nation assuring them that they were guiltless in the death of these men, as it had been ordained by G-d in Elijah's prophecy (I Kings 21).
Yehu struck down Ahab's remaining descendants in Jezreel, as well as Ahab's supporters, until none remained. Yehu was returning to Samaria when he met some relatives of Achaziah, the king of Judah he had killed. Yehu had them captured and killed as part of his purge. (Remember that Ahab's children had married into the royal line of Judah, as well.)
Next, Yehu met Yehonadav, a distinguished person. He asked Yehonadav if he had his support. When Yehonadav said yes, Yehu brought him into his chariot. They came to Samaria where Yehu finished the job of wiping out Ahab's heirs. He then did a seemingly-bizarre thing. "Ahab only worshipped Baal a little," he proclaimed. "Just wait until you see how much I'M going to worship Baal!" He called all the priests of Baal to him, but he was really "working undercover" in order to trap them. He called a big "Baal festival" and Baal-worshippers came from all over the country to the Temple of Baal in Samaria. No G-d-worshippers allowed. Yehu gave each attendee a special garment to wear (this enabled them to be identified). Yehu posted 80 guards and charged them, on pain of death, not to let any of the Baal-worshippers escape. Yehu waited until after the sacrifice was completed, then he had his men strike them down. They burned the idols and demolished the temple of Baal. The site where it stood was turned into a public restroom, for good measure.
He may have destroyed the worship of Baal in Israel, but Yehu left the golden calves of Yeravam in place. His intention wasn't religious but political: like Yeravam, he didn't want the Jews of Israel going to the Temple in Judah. Nevertheless, this was a grievous oversight. However, he had done very well in destroying the house of Ahab and the worship of Baal, so G-d sent word through a prophet (Rashi says Jonah again) that Yehu's dynasty would last four more generations. With this assurance, he could have then safely removed the golden calves without fear, but he still didn't. This displeased G-d, which led to Yehu's kingdom being weakened, not strengthened. Chazael, king of Aram, started making incursions on Israel's borders.
Yehu reigned 28 years and was succeeded by his son Yehoachaz.