A secret experiment that Lex is conducting at LuthorCorp goes terribly awry and causes the release of a dangerous toxin into the air. Smallville residents infected by the toxin -- including Clark, Lana, Lex and Jason -- imagine their greatest fears coming true and lapse into a coma. Desperate to find a cure, Clark gives some of his blood to Lex and is stunned at what his friend does with the antidote.

Season 4 | Episode 10

Allison Mack

as Chloe Sullivan

Annette O'Toole

as Martha Kent

Erica Durance

as Lois Lane

John Schneider

as Jonathan Kent

Kristin Kreuk

as Lana Lang

Michael Rosenbaum

as Lex Luthor

Tom Welling

as Clark Kent