1 Kings 1:41 Adonijah and all the guests who were with him heard it as they were finishing their feast. On hearing the sound of the trumpet, Joab asked, “What’s the meaning of all the noise in the city?”

42 Even as he was speaking, Jonathan son of Abiathar the priest arrived. Adonijah said, “Come in. A worthy man like you must be bringing good news.”

43 “Not at all!” Jonathan answered. “Our lord King David has made Solomon king. 44 The king has sent with him Zadok the priest, Nathan the prophet, Benaiah son of Jehoiada, the Kerethites and the Pelethites, and they have put him on the king’s mule, 45 and Zadok the priest and Nathan the prophet have anointed him king at Gihon. From there they have gone up cheering, and the city resounds with it. That’s the noise you hear. 46 Moreover, Solomon has taken his seat on the royal throne. 47 Also, the royal officials have come to congratulate our lord King David, saying, ‘May your God make Solomon’s name more famous than yours and his throne greater than yours!’ And the king bowed in worship on his bed 48 and said, ‘Praise be to the Lord, the God of Israel, who has allowed my eyes to see a successor on my throne today.’”

49 At this, all Adonijah’s guests rose in alarm and dispersed. 50 But Adonijah, in fear of Solomon, went and took hold of the horns of the altar. 51 Then Solomon was told, “Adonijah is afraid of King Solomon and is clinging to the horns of the altar. He says, ‘Let King Solomon swear to me today that he will not put his servant to death with the sword.’”

52 Solomon replied, “If he shows himself to be worthy, not a hair of his head will fall to the ground; but if evil is found in him, he will die.” 53 Then King Solomon sent men, and they brought him down from the altar. And Adonijah came and bowed down to King Solomon, and Solomon said, “Go to your home.”

If he's worthy... if there's no evil found in him.... oh his goose is cooked.

This is from the easy English site.

Zadok made Solomon king before Adonijah and his guests had finished their large meal. Joab was very afraid when he heard the sound of the trumpet. Adonijah thought that Jonathan had come with good news. Instead Jonathan told him that Zadok and Nathan had made Solomon king. Solomon had ridden on the king’s mule. This was a clear sign that he was now king. He also sat on the king’s royal seat. King David was glad that Solomon was king. Now Adonijah knew that he would not become king.

Adonijah’s guests left quickly. They were afraid that people would punish them. This was because they had helped Adonijah. Adonijah went to hold the corners of the altar. Exodus 21:14 says that a person would be safe there. However, that was only true if they had not intended to kill someone.

Although Adonijah intended to kill Solomon, Adonijah was not yet guilty of murder. But Adonijah was guilty of other crimes. He had not respected his father, David. Instead, Adonijah had even plotted a revolution against him. David and Solomon were kings whom God had appointed. So when Adonijah tried to appoint himself to be king, he was acting against God. So Adonijah was plotting to destroy God’s purposes.

Adonijah’s actions were terrible, but Solomon decided not to make a judgement about Adonijah’s crimes. Instead, Solomon was wise. He made a sensible political decision. He knew that many people liked Adonijah. So Solomon simply told Adonijah that he must be loyal. If Adonijah obeyed, he would not die.

So it's a play on words. Solomon knew that Adonijah would not be loyal. Solomon knew Adonijah. Adonijah was his brother from another mother. David himself was a womanizer and a murderer. Adonijah was David's son... and the apple doesn't fall from the tree, right?

This is from blueletterbible.org.

So that all the city is in an uproar: This was very distressing to Adonijah. He had the support of some important powerful men (those attending his banquet), but now he knew that the heart of the people belonged to Solomon.

Also the king said thus, "Blessed be the LORD God of Israel, who has given one to sit on my throne this day, while my eyes see it!" This told Adonijah that even King David was completely behind Solomon. There was no hope for his future as king.

All the guests who were with Adonijah were afraid, and arose, and each one went: They came for a nice dinner, and to support Adonijah. They left quickly as soon as it was clear that he would not and could not be king. Now it was dangerous to say that you supported Adonijah as king.

Finally, this is from Bible.org.

The entire city celebrated the new King. A messenger went to Adonijah’s feast and told him that Solomon was the new King. Ask: How do you think he took this news? Listen for answers. Say: He was gripped with fear. He was afraid that Solomon would have him killed. Adonijah went from being cocky and full of himself to being scared to death in a matter of seconds! All of his guests were also panic-stricken. They took off to their homes. They didn’t want to be known as the people who were enemies of the new King!

Adonijah ran to the tabernacle and pleaded for the Lord to spare his life. When Solomon heard about his brother cowering in fear, he sent a message to him.

So... Behave yourself Adonijah.... and not a hair on your head will be harmed....

Oh his goose is so cooked....