An episode of unknown number from the Original Series.
The NSEA Protector butts into an impenetrable magnetic shield with reflective qualities. As the crew tries to figure how to penetrate the wall, there's a slight shift in magnetic alignment and Lt. Madison falls to the other side through a crack in the time-space continuum. As always, our good Commander must save Lt. Madison, by blasting through the shield, or traveling eons in the other direction to find her. He finds a crack in the mirror by facing his worst fear - the fear that though he has repeatedly shown valor in the line of duty, he will one day lack courage at a crucial moment.