Not much is known about the Old Ones, the ancient but highly advanced race that once inhabited the planet Exo III. What little we do is learned by Captain James T Kirk when the Federation starship USS Enterprise is sent to the planet in search of the renowned research scientist, Dr Roger Korby.

Exo III lies in a remote sector of the Alpha Quadrant, well off normal space trade routes, so Dr Korby and his research team are isolated on the planet for several years.

Beaming down to the surface with Nurse Christine Chapel, who is Dr Korby`s fiancee, Kirk finds a desolate, icy world. Exo III is an old planet circling a dying sun. Eons ago, the inhabitants retreated from the frozen surface to seek refuge in underground caverns.

The natural caverns honeycombed beneath the surface have been modified and expanded by the Old Ones. Kirk is only able to see a small part of what must once have been a remarkable underground metropolis.

Virtually all we know of the Old Ones history on Exo III comes from their creations, and androids who were built to serve them.

When Dr Korby first arrived on the planet, and discovered the underground caverns, he found no Old Ones alive. Their only remaining presence was the legacy they left behind; incredible biotechnical machines, and a city which still functions.

There is only one android still left on the planet, who calls himself Ruk. He has toiled here for so long, tending the intricate machinery necessary to maintain life support and other systems, that even he cannot remember the exact timespan.

Ruk remembers only his duties and the primal command which was programmed into him by the Old Ones; protect. And that is what he has been doing, protecting the city and the machines against outside intruders, at any cost. Kirk learns this all too well when the two security guards who beam down with him from the Enterprise are killed by the formidable android.

Kirk realises that the only chance for his survival lies in gaining knowledge of the true identity of the Old Ones, and learning what caused them to abandon their planet. Ruk, supplies the answers to Kirk`s questions.

The Old Ones invented the androids and built many of them to service their race. That the androids are humanoid in appearance appears to indicate that the Old Ones themselves were likewise humanoid. The design and layout of the underground city would further suggest that they were similar in size to standard humans.

Ruk, the last android, is much larger than most humans, but his size is probably related to the strength he needs for his tasks rather than being an imitation of the Old Ones.

While the Old Ones came to depend upon the androids, they also began to fear them. In creating such sophisticated beings, the Old Ones had accomplished something too perfect. The androids were more than mere machines; they had become sentient, with emotions and aspirations.

BY the time the Old Ones realised this flaw in their servants, it was too late. They began to turn off the androids, but their creations rebelled. The androids had been programmed to protect and obey the Old Ones, but there was an even greater equation; existence overrides obedience. The androids turned on their masters, and destroyed them.

When Dr Korby`s ship crashlanded on the planet, he was the only survivor, but he was badly injured. He used his remarkable intellect to construct an android version of his assistant, and even transferred his own mind from his dying body into an android replica of himself.

Eventually Korby diiscovers the Old Ones major flaw; their arrogance. He realises that the androids are themselves fatally flawed, operating by pure logic rather than emotion. In a final selfless act, Korby destroys the remaining androids and the mechanical body that houses his won human mind. With no one left to tend their subterranean metropolis, the Old Ones are left to fade into history, with only a dead city on a frozen world to mark their passing.