Here’s the official synopsis from the CW for the next new episode of Smallville entitled "Hex":
IT’S FREAKY FRIDAY FOR CHLOE AND LOIS WHEN DC CHARACTER ZATANNA APPEARS
At Chloe’s (Allison Mack) birthday party, a mysterious magician named Zatanna (guest star Serinda Swan) grants Chloe’s wish to be more like Lois (Erica Durance) and switches the two into each other’s bodies. Zatanna searches for her father’s book of spells so she can conjure up his spirit but not before also granting Clark (Tom Welling) his deepest wish. Aaron Ashmore and Justin Hartley also star. Mairzee Almas directed the episode written by Bryan Q. Miller.