For many years, a strange epidemic of insanity has slowly but surely made its way through an interplanetary system and the planet Deneva is right in the path. The Enterprise tries to contact a Denevan ship that seems intent on flying straight into the sun. The only broadcast they're able to get from the ship is the eerie chant of "Free! I'm free at last!" before the entire ship and its pilot disintegrates in the radiation of the sun. Tropes for this episode include: