Romulan Commander
Mark Lenard

Decius
Lawrence Montaigne

Centurion
John Warburton

Lt. Andrew Stiles
Paul Comi

Lt. Robert Tomlinson
Stephen Mines

Ensign Angela Martine
Barbara Baldavin

Commander Hansen
Gary Wallberg

While on patrol along the Federation - Romulan Neutral Zone the Enterprise receives a distress call from Outpost Four. A Romulan Bird-of-Prey is attacking it and, despite warning challenges from the Enterprise, destroys the outpost with an energy plasma blast. Following this the Bird-of-Prey disappears under cover of its cloaking device to make its escape but the energy consumption of the shielding is so high that the Romulans cannot use their sensors to determine the location of the Enterprise.

A momentary sensor blip on heading 111 mark 14 alerts Kirk to its position and he orders Sulu to steer a parallel course, but the Romulan commander foresees this and they lose track of the vessel again. Kirk waits patiently for the ship's reappearance, guessing that it will come back to try an attack on the Enterprise and that it will have to de-cloak first in order to have enough power for its weapons.

He is correct, and scores a direct hit on the Romulan ship when it shows itself, but not before his own vessel is damaged. Kirk commands that the Enterprise 'plays dead' and both ships hang in space each waiting for the next action from the other. During this 'cat and mouse' game Lieutenant Commander Stiles comments on Spock's similarity in appearance to the Romulans and speculates on his trustworthiness. This was the first time that the Romulan race had actually been seen, all previous contact having been carried out via subspace radio.

The commander of the Bird-of-Prey ejects a consignment of damage debris and dead bodies which conceals a nuclear device. The Enterprise's sensors detect it late and Kirk, on destroying it, causes further damage to his injured vessel. Spock and Stiles happen to be in the phaser room at the time and when a vapour leak, caused by the explosion, overcomes Stiles Spock drags him to safety, earning the trust and respect of the man. Now running short of fuel, with little chance of either defeating the Enterprise or returning home, the Romulan commander chooses to destroy his ship and crew rather than suffer the shame of being captured by the Federation.