Smallville: Season 5, Episode 22

5 - 22: Vessel

When Lex is possessed by Milton Fine and Fine's master, Clark must make a sacrifice and a decision, a decision that will affect those closest to him. Meanwhile, Milton Fine unleashes a deadly virus that affects millions, and Jor-El channels himself through Lionel to warn Clark of the coming destruction of Earth's population in a climactic battle of good versus evil.