Stardate 6770.3: The USS Enterprise is escorting Commodore Robert April and his wife Dr. Sarah April, the first captain and chief medical officer of the ship, to Commodore April's retirement ceremony on Babel. While en route, Kirk attempts to rescue an alien vessel which is heading towards the Beta Niobe nova at Warp 36. But the alien ship drags the Enterprise inside the nova too, and they end up in a universe where everything works in reverse order. The alien from this negative universe, Karla Five, agrees to sacrificing her ship to ignite a star in her negative universe that corresponds to a nova in the positive universe which could then serve as a gateway. While everyone aboard is growing younger, Commodore April assumes command and the Enterprise safely returns to its own universe.

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