Page "Where No Man Has Gone Before" Paragraph 5

Alarmed that Mitchell may take over the Enterprise, Kirk decides to maroon him on an unmanned lithium-cracking facility on the remote planet of Delta Vega.

Once there, the landing party tries to confine Mitchell, but his powers have become great.

He goes on a rampage, kills navigator Lt. Lee Kelso and escapes, taking with him Dr. Dehner, who has now developed similar powers.