Smallville - Season 3 - Eps 19: Memoria
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.
About Smallville

Title: Smallville
First Air Date: 2001-10-16
Last Air Date: 2011-05-13
Status: Ended
Rating: 8.2/10 (from 4151 votes)
Language: EN
Seasons: 11
Total Episodes: 216
Network: The WB The CW
Genres: Sci-Fi & Fantasy, Action & Adventure, Drama
Production Companies: DC, Warner Bros. Television, Tollin/Robbins Productions, Millar Gough Ink
Synopsis
The origins of the world’s greatest hero–from Krypton refugee Kal-el’s arrival on Earth through his tumultuous teen years to Clark Kent’s final steps toward embracing his destiny as the Man of Steel.
Cast

Tom Welling
Clark Kent

Erica Durance
Lois Lane

Cassidy Freeman
Tess Mercer

Justin Hartley
Oliver Queen