S03E17: Legacy

When Jonathan begins to act strangely, Clark believes Jor-El is sending Jonathan messages through the key and is the cause for his father's withdrawal from the family. Clark goes down to the caves to confront his biological father but Lionel catches him there and begins putting the pieces together, leading him straight to Dr. Swann. As the two billionaires face off, a deal is struck and Lionel's true motives are revealed.