Smallville - Season 4, Episode 16
Lois' (ERICA DURANCE) younger sister, Lucy (PEYTON LIST), with whom Lois doesn't get along, visits Smallville and charms everyone she meets. However, Clark discovers a darker side to Lucy after he catches her stealing money from a bar. Clark forces Lucy to reveal the truth about her sudden appearance in town -- a truth that puts Lois in grave danger. Meanwhile, the crystal disappears from Lana's apartment, and Jason accuses Lionel of stealing it.