Season 2, Episode 23
Production episode: 2×25
Original air date: March 1, 1968
Star date: Unknown
As the Enterprise approaches the planet Omega IV, they notice another vessel in orbit. It appears to be a Constitution-class starship, the USS Exeter, but it won’t respond to any hails. Kirk, Spock, McCoy, and Lt. Galloway (start your redshirt timer…) beam over to the ship. They discover… nothing. The ship is empty. All they see are uniforms lying around, filled with some kind of white crystals.
MCCOY: These white crystals. That’s what’s left of the human body when you take the water away, which makes up ninety-six percent of our bodies. Without water, we’re all just three or four pounds of chemicals.
Uh, no one tell his high school science teacher, OK? (We’re about 70% water.) They play the final log tape, the “Surgeon’s Log.” They see a haggard and visibly suffering ship’s surgeon on the viewscreen explain that they’ve all been infected with some kind of virus. That virus will have also infected Kirk and anyone else onboard the ship. Their only hope is to beam to the surface. He then collapses dramatically.