Lazarus
Robert Brown

Lt. Charlene Masters
Janet MacLachlan

Commodore Barstow
Richard Derr

Lt. Leslie
Eddie Paskey

The Enterprise is carrying out a survey of an uninhabited planet when it is shaken by a huge disturbance. Spock reports that, according to his sensors, everything within range had ceased to exist for a brief moment of time during which a life form had appeared on the surface of the planet.

A landing party beams down and finds a small craft containing a badly injured being, of human-like appearance, identifying himself as Lazarus. He pleads for help, claiming that he has followed an 'evil thing' down to the planet despite the fact that Spock's scans show no other life forms. Lazarus is taken back to the Enterprise sickbay where he suffers regular convulsions, coinciding with disturbances on the planet, and a wound on his head seems to appear and disappear of its own accord.

Scanning a source of radiation on the surface, Spock concludes that it may be a 'rip in the universe' which they could pinpoint using Dilithium crystals. Lazarus points out that he could use the crystals to defeat his 'enemy' but Kirk refuses to supply him with any. In desperation, Lazarus steals some of the crystals but is soon apprehended, strangely blaming his 'enemy' for the theft. None of the crystals can be found.

After further thought, Spock postulates that the radiation must be coming from a parallel universe, at which point they come to the realisation that 'Lazarus' is, in fact, two different beings who are constantly criss-crossing between them, causing the disturbances they have experienced. Kirk and Spock conclude that if the two of them actually meet it could destroy both universes.

The 'other' Lazarus also manages to steal some of the crystals and escapes back to the surface of the planet. Kirk beams down and finds him mounting the crystals in his disabled ship. He throws himself at Lazarus but, at that moment, there is a shift and he finds himself in the alternative universe. A much quieter, calm Lazarus explains to him that the other one is mad and has his mind set on destroying both universes.

If Kirk can somehow manoeuvre the mad Lazarus into the corridor between the universes and destroy his ship then the other Lazarus will be able to keep him there. Kirk achieves this and the two versions of Lazarus are last seen struggling together in the 'corridor' as the rift heals, sealing them in to battle against each other for all eternity.