What happened to the Israelite who brought a Midianite woman into the camp in the sight of Moses?

Phineas the priest took a spear and thrust a spear into the bodies of both the man and the woman.

What did God do to stop them from sleeping with the Moabite women and worshiping Baal of Peor, and how many died ?

God sent a plague so that those who died were 24,000 in number.