Smallville :

A teenage girl, Amy Palmer,develops an obsession with Lex. But when an invisibility fluid is discovered, an unseen enemy tries to ensure that the world knows that Victoria is the wrong woman for Lex. The situation becomes life threatening as attacks in the Luthor mansion pit Clark against an invisible enemy. Amy is considered the obvious suspect, and evidence seems to implicate her, but the situation is more complicated than it seems.

Meanwhile, Clark is thrilled when Lana seeks his companionship after Whitney inexplicably rebuffs her.