This chapter is like the confluence of several rivers of evil flowing together into a big pile of mess. There are at least 4 different evil parties conspiring together to kill Naboth.
Ahab starts off this chapter just fine; he wants Naboth's vineyard because it is next to his palace and he offers to give him money or better land in exchange for it. That is perfectly reasonable. Naboth refuses, however, because he wants to keep his family's ancestral inheritance. In simple terms, we could say it has sentimental value to him, but given everything we have read about the importance of inheritances and how the land is symbolic of Israel's covenant with God, I'm not at all surprised that Naboth refuses to sell his land.
After this, we see Ahab "vexed and sullen" again, refusing to eat and upset that he has been refused. Like so many other times, he is not acting like a king here. Jezebel also seems embarrassed by Ahab's behavior, and promises to deliver the vineyard to him. This is where Ahab begins to sin, because he knows what Jezebel is like. He knows that she is a murderous woman and by putting the matter in her hands, he effectively signed Naboth's death warrant. Ahab is the first river of evil, weak and indecisive but happy to see innocent men die if it satisfies his desires.
The second river is Jezebel herself, who uses her authority as Ahab's wife to act on his behalf, writing a letter in his name, ordering the leaders of Jezreel to kill Naboth. We know from previous chapters that Jezebel would kill the prophets of the LORD because she desires Baal worship to predominate over Israel. More broadly, Jezebel has no respect for human life, just like her husband. Ahab sins through his passivity, but Jezebel sins actively. It is particularly foul that Jezebel intends to kill Naboth by proclaiming a fast, because fasting is supposed to be a sign of contrition and humility, bowing before God and declaring one's dependence on him. Jezebel intends to use this religious festival as an opportunity to commit murder which shows her basic lack of morality.
Jezebel's incitement flows into the third river, which is the elders and nobles of Jezreel. When ordered by Jezebel to kill Naboth, they obey her without objection. I think this is a very clear example of how evil at the highest levels of power (with the royalty, Ahab and Jezebel) flows down and corrupts the authorities under them. Why do all the elders obey Jezebel's clearly evil order? Because all of the elders who would have resisted her must have been replaced or killed earlier in Ahab's reign. There is a cultivation and grooming that happens over time when leaders use their authority to build patterns in the organizations under them by rewarding the people who share their values and punishing or demoting the people who resist them. This has many practical implications, but in the immediate case, what it means is that Jezebel has elevated authorities in every town that are just as violent as she is.
The fourth, and final river, are the two false witnesses, whom the text calls "worthless men". At every other layer (Ahab, Jezebel, the elders and nobles), the people sinned through conspiracy to commit murder, but did not lay their hands on Naboth. These two men commit the fatal act by bearing false testimony against Naboth and sealing his death. These men would not have acted if they were not commanded by the authorities, who themselves were under Jezebel's authority, who herself was acting because Ahab permitted her to do so through his passivity.
When Ahab finds out that Naboth was dead, he once again shows the evil in his heart by going down to take possession of Naboth's vineyard (v. 16). In this act, he shows that Jezebel acted in accordance with his will, even though superficially Ahab could claim that he was innocent in Naboth's death. Nevertheless, the LORD holds him responsible for murder (v. 19).
In the place where Elijah finds Ahab, the first thing Ahab says is that Elijah is "my enemy". This is a remarkable statement, and it shows just how skewed Ahab's perspective was. Ahab says that Elijah is his enemy, but the truth is that it is the LORD who is Ahab's enemy, because Ahab is persisting in doing evil. Ahab made the LORD into his enemy by acting in rebellion against the LORD. Elijah resists Ahab because Elijah lives under the authority of the LORD, but Ahab is deceived if he thinks that Elijah is his problem.
Lastly, and in quite a remarkable turn, Ahab actually repents of the evil he did and he fasts, not the deceitful fast that was used to kill Naboth, but a sincere, repentant fast. And just as remarkably, the LORD changes his mind (to an extent) against punishing Ahab. Ahab has sinned in so many ways and for so long, it is almost unthinkable that he would repent, and yet here we are. And I think it is stunning that the LORD would respond to that and show kindness, but that is exactly what God does because that is who he is. In Exodus 34:6, God declared his nature: "The LORD, the LORD God, compassionate and gracious, slow to anger, and abounding in love and truth." When God says that he abounds in compassion and grace, that is for all men and women on the earth, from the righteous Elijah to the evil Ahab. God showed kindness to Elijah by preserving him in the wilderness, and he shows kindness to Ahab by accepting his repentance, and even by sending Elijah to confront and threaten him. Without the threatened judgment from Elijah, Ahab would not have repented. In my opinion, even Elijah's ministry itself is an act of kindness to Ahab because it is through Elijah that Ahab came to repentance, extending his life.