ENT: Impulse

The Enterprise receives a distress call from a Vulcan ship formerly lost in the Expanse. When the landing party arrives, they discover they have walked into a Romero like setting of crazy, pustulant Vulcans. As their Night of the living Vulcans continues, Phlox discovers the Vulcan madness is caused by Trellium D, the only substance which can shield the ship from the Expanse's anomalies. The episode ends with Archer assuring T'Pol they will find a way to shield the ship AND keep her sane.