Genesis 12

Abram was afraid that the king in Egypt would kill him because his wife Sarai was beautiful (v11-12)
The king took Sarai as wife and terrible diseases was sent on the king and the people of his palace (v17)

Now.. it was Abram who lies, who uses his own way to protect himself, who sends his own wife to another man, and receives many gifts. Abram is the one who sin. Why the king got punished? He does not know Sarai is Abram's wife but thinks she is his sister.
I don't understand, didn't we just read yesterday, that sin is not counted where there is no law? (Romans 5:13)