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

Chloe Sullivan

Annette O'Toole

Martha Kent

Erica Durance

Lois Lane

John Schneider

Jonathan Kent

Kristin Kreuk

Lana Lang

Michael Rosenbaum

Lex Luthor

Tom Welling

Clark Kent