Star Date: 5730.2 Location: Somewhere in the galaxy

The U.S.S. Enterprise, under the command of Captain James T. Kirk, is on a mission to investigate a planet with strange energy readings. On the world, they encounter two aliens, Bele (Frank Gorshin) and Lokai (Lou Antonio), who are locked in an eternal battle with one another.

The crew of the Enterprise quickly discovers that Bele and Lokai are the last survivors of their planets, Cheron and Andor, respectively. Both planets have been destroyed in an intergalactic civil war between the two races. Nevertheless, the two aliens have survived for centuries, each pursuing the other across the galaxy but never managing to defeat their enemy.

The female characters in the episode include Uhura (Nichelle Nichols), Rand (Grace Lee Whitney), and Yeoman Barrows (Barbara Baldavin). Rand is a new character in the episode, and she serves as a technical officer and communications expert. Uhura and Barrows assist in hosting the planet's inhabitants on board the Enterprise.

The antagonists are Bele and Lokai, who continue to fight each other, despite the Enterprise's efforts to get them to make peace. Captain Kirk attempts to reason with them but fails as the two aliens cannot reach a consensus.

The episode also features a romantic plot between Captain Kirk and Uhura. Although the two never explicitly confirm their romantic feelings for one another, their chemistry is undeniable.

In the end, the crew of the Enterprise manages to find a way to separate Bele and Lokai, allowing them to continue their battle without causing further destruction. Meanwhile, Captain Kirk and Uhura's relationship continues to build.

Grace Lee Whitney became a successful actress in her own right with roles in films like Grease and in television shows like Roseanne. Nichelle Nichols also had a very successful entertainment career, appearing in films like Star Trek IV: The Voyage Home and television shows like The Fresh Prince of Bel-Air.

Interestingly, "Let That Be Your Last Battlefield" was the last episode of Star Trek: The Original Series to be filmed.