S4, E6: Clark hears a painful ringing sound and is compelled to go to the penitentiary that houses Lionel. When he sees Lionel attempt to stab Lex with a strange glowing stone, Clark grabs for the rock causing Lionel and Clark to switch bodies. After learning his new body has superpowers, Lionel immediately begins wreaking havoc on Smallville. Trapped in prison without his powers, Clark must find a way to get his body and powers back in order to save his friends and family.