There are eleven verses about Angels in the book of Numbers. Ten of those verses are in the story of Balaam. The eleventh is the first one and is in Numbers 20:16.
“And when we cried unto the Lord, he heard our voice, and sent an angel, and hath brought us forth out of Egypt: and, behold, we are in Kadesh, a city in the uttermost of thy border:”
This verse is a retelling of Exodus 14:19-20, where an Angel of God, went before to lead and went behind to protect the Hebrews from the Egyptians. Apparently the Lord sent an Angel of God,
Now Balaam, and the talking donkey: Balak the King of the Moabs, sent men to Balaam, to ask him to curse the Hebrews. God came to Balaam to guide him in the way he should go. Please read chapter 22.
God sent the Angel of the Lord, to deal with Balaams disobedience.
“And God’s anger was kindled because he went: and the angel of the Lord stood in the way for an adversary against him. Now he was riding upon his ass, and his two servants were with him. And the ass saw the angel of the Lord standing in the way, and his sword drawn in his hand: and the ass turned aside out of the way, and went into the field: and Balaam smote the ass, to turn her into the way. But the angel of the Lord stood in a path of the vineyards, a wall being on this side, and a wall on that side. And when the ass saw the angel of the Lord, she thrust herself unto the wall, and crushed Balaam’s foot against the wall: and he smote her again. And the angel of the Lord went further, and stood in a narrow place, where was no way to turn either to the right hand or to the left. And when the ass saw the angel of the Lord, she fell down under Balaam: and Balaam’s anger was kindled, and he smote the ass with a staff.”
The Lord then opened Balaams eyes.