With deuterium fuel dwindling to nothing, the U.S.S. Voyager lands on a "demon" planet — so-called because its environment is toxic to human life — to collect from its vast deuterium lode. Both Tom Paris and Harry Kim are suited up in protective gear and sent out to collect the precious deuterium, but return without their protective suits. Instead, it is now the U.S.S. Voyager's environment that is poisonous to them.

Alexander Enberg (Ensign Vorik)

• The ship goes to "grey mode," where all non-essential systems are shut down and the rest run at 20%.
  
• "Demon"-class is the common name for Class-Y planets.
  
• Deuterium is a hydrogen isotope. It is the primary fuel source for the fusion reactors and is used as the matter in the matter/antimatter warp reactor. (Anti-hydrogen is the anti-matter.) The fusion reactors drive the impulse engines and the thrusters.
  
• Voyager makes a rare emergency landing on the planet.
  
• The "silver blood" became sentient when Tom and Harry touched it. The crew agrees to let the fluid make duplicates of themselves, who remain on the planet. The duplicates will reappear in the 5th season episode "Course: Oblivion".