"Riddles" - Attack on Tuvok renders him useless while Janeway chases shadow people for remedy.
During negotiations with the Kesat government, Tuvok is zapped by a powerful energy force, suffers severe neurological trauma and emerges as a mere shell of his former self while Janeway searches for the mythical species responsible for the attack in hopes of finding a cure.
While the optimistic Neelix keeps pushing to restore the mental prowess of the confused Tuvok, Janeway works with Naroq, a Kesat inspector, as they try to solve the enigma of the cloaking device used by the hostile Ba'Neth -- or "shadow people" --who seek Voyager's technical data. Even as the crew pursues the elusive Ba'Neth for a solution to Tuvok's misfortune, the suddenly vulnerable Vulcan discovers emotions he never could appreciate before.
Starring Kate Mulgrew as Captain Janeway, Robert Beltran as Chakotay, Roxann Dawson as B'Elanna Torres, Robert Duncan McNeill as Tom Paris, Ethan Phillips as Neelix, Robert Picardo as The Doctor, Tim Russ as Tuvok, Jeri Ryan as Seven of Nine, Garrett Wang as Harry Kim.
Guest Starring Mark Moses as Naroq.
This episode was directed by Roxann Dawson. The story was by Andre Bormanis. The teleplay was by Robert Doherty.
TV Guide online synopsis: Janeway and a Keset agent rush to uncover why a mysterious energy force is causing Tuvok's Vulcan physiology to endure severe neurological trauma in the form of mental distress and emotional unpredictability.