STAR TREK: #20 The Alternative Factor, 1967

Writer: Don Ingalls
Director: Gerd Oswald

Captain Kirk: William Shatner
Science Officer, First Officer, Cmdr. Spock: Leonard Nimoy
Dr. Leonard "Bones" Mc Coy: DeForest Kelly
Lt. Sulu: George Takei
Lieutenant Commander Montgomery Scott: James Doohan
Lieutenant Uhura: Nichelle Nichols

Lazarus A and B: Robert Brown
Lt. Charlene Master: Janet MacLachien
Commodore Barstow: Richard Derr

Stardate 3087.6

The Enterprise is orbiting a planet without life forms as they experience a moment of "nonexistence" – throughout their known world. Kirk is ordered to investigate where that came from, because it is suspected to be part of a plan for invasion of the Federation. Soon Spock detects a life form on the plant. There Kirk finds a man called Lazarus, who tells Kirk that the effect was caused by his enemy, who is after dilithium crystals. On board, Lazarus seems to change frequently. At some stage a wound appears and is gone another moment. So change his behavior patterns. 

Lazarus manages to come onto the bridge and he disagrees with the captain. When he is sent away with a guard, the Guard is overwhelmed and the dilithium is missing. On pursue back on the planet, Kirk discovers that Lazarus is two people - one sane and one from an anti-matter universe. The transfer from the other universe of the second Lazarus had caused the moment of nonexistence. If both remained together in one universe, both universes cannot exist. With the help of Kirk the sane Lazarus traps his counterpart in an intermediate time corridor where no harm can be done to either universe, but the two of them will have to fight forever.

Pictures courtesy of All Star Trek