A Medusan ambassador is carried aboard in a box, and his form can drive observers mad.
The Enterprise carries Ambassador Kollos, a Medusan whose true form is so alien that humans who see it go mad, so he travels in a protective box. Among his companions is the telepath Miranda Jones, who guards him and has her own reasons for wanting to stay close. Spock, who must pilot a vessel with Kollos, risks his sanity.
The story explores prejudice and the human difficulty in accepting the truly different, using the idea of infinite diversity in infinite combinations. It also features Spock wearing a visor and a sharp love triangle. Fans recall the unusual premise and its message about beauty.