Plot

The Enterprise must decide on its response when a Romulan ship makes a destructively hostile armed probe of Federation territory.

The Enterprise answers a distress call from Federation Outpost #4, a monitoring station on the Federation side of the neutral zone with the Romulan Empire. The outposts were established over a century ago and no one has actually seen a Romulan. The Romulan vessel seems to have some type of high energy explosive device as well as a cloaking device to make the ship invisible. When it appears that Romulans bear a strong resemblance to Vulcans, Kirk must deal with a rebellious crew member. He must also engage in a dangerous cat and mouse game with a very intelligent Romulan commander.—garykmcd

Outposts along the neutral zone abutting Romulan space have been vanishing. When Outpost #4 next falls under attack, it becomes clear that a Romulan ship is testing new weapons against the Federation. No human's ever seen a Romulan before, and the first sight of one, bearing a strong resemblance to Vulcans, has some worried that there are traitors already within the Federation (namely Mr. Spock). Kirk must deal with these divisive suspicions amongst the crew as the Enterprise fully engages the Romulans and its seasoned commander in a battle of wits and tactics that could leave one or the other or both ships' crews dead.—statmanjeff

This episode begins with a wedding between Lt. Tomlinson (Stephen Mines) and Lt. Angela Martine (Barbara Baldavin). They are at the chapel standing side by side, Tomlinson in his uniform, and Angela in her nice uniform with black leggings and boots. Kirk is performing the ceremony. (chaplains are not permitted on war vessels. The Captain must preside).

They receive a distress call from Earth Outpost 4, which is under attack. Kirk orders battle readiness and goes to rescue Earth Outpost 4, which is in the neutral zone between Federation and ROmulan space. The neutral zone was established after the last Earth-Romulan war which was fraught with nuclear weapons. Entering the zone was to be considered an act of war. Kirk is clear that to prevent inter-planetary war, the outposts and the ship are considered expendable. The last war was more than a 100 yrs old and no one knows what a Romulan war ship looks like. and there are no visuals on any Romulans either.

From attack on the outposts, Kirk and Spock learn that the ROmulans need to de-cloak their ship in order to fire, making them visible for brief periods. Spock and Kirk also theorize that the cloaking device takes too much power from the ship's engines. Enterprise starts tracking a ship near Outpost 4 who is now moving across the Neutral zone. They get visuals from the ship and see that Romulans look like Vulcans. The whole ship turns against Spock. The Romulans pick up the Enterprise on their sensors. It is shown that the Romulan commander understands Kirk's maneuvers and knows that if Kirk follows the Romulans into the neutral zone, it will be shot and a war will start. The Romulan Commander doesn't want another war.

On Enterprise Spock is aware of the Vulcan and Romulan colonizing past. He says Earth needs to show courage and thus attack is the best option. As Enterprise prepares to attack, the Romulan Commander understands Kirk's plan and attacks first. Kirk evades their attack by reversing. The Romulan commander goes back on the path to the neutral zone, but this time Kirk decides to follow it, violating the peace treaty. In the neutral zone, the Romulan tries to fake its destruction by throwing debris out of its tubes, but Spock spots the ruse. However Spock has lost track of the Romulans and thus a wait and watch ensues.

Kirk outsmarts the Commander and attacks the Romulan ship, but this time the COmmander puts a nuclear device in the tubes with a proximity fuse. As Enterprise moves closer, the warhead explodes and damages the Enterprise badly. Aboard the Romulan ship, which possesses a 'cloaking device' to make it invisible, the men tell their Commander "We must go for the kill! A Federation star-ship is a great prize. We will be honored when we return." But the Commander (Mark Lenard) knows they are low on fuel, and weary from battles. He wants to bring his ship and crew home safely. But the men keep saying "We must destroy the Enterprise." (Also, there are no women on the Romulan vessel, as there are on the Enterprise).

Meanwhile, Kirk's ship is badly damaged, and Kirk decides to keep the power low, to pretend to be "dead in the water" to bait the Romulans. The end is near. Suddenly there is an explosion in auxiliary control, where Mr Stiles (Paul Comi) has been working with another crewman. Mr Stiles is a very prejudiced man. He has been making accusations about Mr Spock, because he looks just like the enemy, because of his ears. He accuses Spock of being a spy. That is why Kirk sent him on the repair mission. After the explosion, there is smoke pouring out of the auxiliary control room. Mr Spock is passing by and sees the smoke. He runs in and is choking, and pulls one of the men out safely, but the other chokes to death.

On the bridge, Kirk's plan is working. The Romulan commander is baited, and Kirk waits for him to bring his ship close and for him to turn off the cloaking shield, so to be able to fire torpedoes. Kirk waits till the last second, and commands "Fire!!" The Enterprise phasers cripple the Romulan ship. He radios the Commander, who he sees on the view-screen, standing, near death, among his dying crew.

"Beam your survivors here," says Kirk. "We are merciful to prisoners". Kirk was not lying. But the Commander is a good soldier and says "It is not our way." Then he detonates his own ship with all of the remaining crew on board. McCoy reports in from Sickbay on the intercom. "Spock and Mr. Stiles are recovering," McCoy says. "But we have one casualty from the explosion in the control room." Lt. Tomlinson is dead.

Kirk is devastated. He goes to see Angela in the wedding chapel. She is crying. He tells her things to make her feel better. There will be no wedding, only mourning. Luckily, in the next episode,"Shore Leave", Angela has a new boyfriend named Esteban, so all is resolved.