Episode 63 of "Smallville"
s03e19 Memoria
Title: Memoria
Original Air Date: 04/28/2004 on WB
Director: Miles Millar
Writer: Alfred Gough, Miles Millar
Guest Stars: Elizabeth Thai (Luthor Nanny), Kendall Cross (Voice of Lara), Andrew Airlie (Mr. Woodward), Martin Cummins (Dr. Garner), Alisen Down (Lillian Luther), Matthew Harrison (Garner's Assistant), Wayne Dalglish (Young Lex)
Plot Outline:
Believing that key information about his father's past was lost when his memory was erased, Lex decides to join an experimental program with Dr. Garner to regain the information so he can turn his father over to the FBI. Knowing that Lex will discover his secret if he regains his memory, Clark tries to stop him but is caught by Lionel and the doctor and exposed to the same radical treatment so that Lionel can solve the mystery of Clark's past.