Seasons & episodes

S1 · E25The Devil in the Dark 1967-03-09 · 50 min＋

Kirk investigates a series of grisly murders on a mining planet that are the work of a seemingly hostile alien creature.

S1 · E26Errand of Mercy 1967-03-23 · 50 min＋

The Federation and the Klingon Empire teeter on the brink of war as Kirk investigates Organia, a humble planet, inhabited by pacifists, that is unwittingly caught in the middle.

S1 · E27The Alternative Factor 1967-03-30 · 51 min＋

Kirk and Spock encounter an alien named Lazarus who claims to be from an anti-matter universe.

S1 · E28The City on the Edge of Forever 1967-04-06 · 50 min＋

Kirk and Spock must travel into the past in order to correct a change that will alter history.

S1 · E29Operation: Annihilate! 1967-04-13 · 50 min＋

Kirk and the Enterprise must combat parasitic aliens threatening the lives of millions.