Archer invites Reed to breakfast, hoping to become better acquainted with his armory officer. Reed, however, seems reluctant to discuss anything other than work. Just as Archer's getting frustrated, T'Pol alerts the captain that an uncharted system has been detected and one of the planets is Minshara-class. As Enterprise enters the planet's orbit, it is rocked by massive explosions, damaging sections of the ship and injuring several crewmembers, including Hoshi. Reed is able to discern that the ship has been hit by an alien orbital mine, which has attached itself to the hull. As the mine has the power to disable Enterprise, Reed suits up and heads out to defuse it. Uncertain that Reed will succeed in his task, Archer suggests an alternate plan to Trip — detach the section of hull plating surrounding the mine, allowing it to drift away. Trip notes that this will expose a good portion of the impulse manifold, but Archer tells him to get started on it anyway — the captain will consider the plan a last resort.

As Reed works, he suddenly becomes aware of a strange alien vessel de-cloaking nearby. The ship hails Enterprise, but the translator can't quite get a lock on the strange language, and Hoshi is out of commission in Sickbay. The aliens begin to fire warning shots at Enterprise, so Archer orders Mayweather to move them out of harm's way — slowly, so as not to injure Reed, still hard at work on the hull. Mayweather must also be careful not to collide with any of the other mines in the field.

Reed begins to make some headway in his efforts to disarm the mine, but just as he's making progress, the motion from Enterprise jostles the mine. A spike thrusts out of the mine and through Reed's leg, pinning him to the ship's hull. Hoping to disarm the mine and save his officer, Archer heads out to the hull. With Reed unable to reach the mine, Archer must depend on him for instructions to disable it. Reed thinks it's too dangerous, but Archer insists that he's a quick study.

Meanwhile, Hoshi is translating the mysterious alien language from Sickbay. The aliens have ordered Enterprise to leave immediately or be destroyed — they have annexed the planet in the name of "The Romulan Star Empire." Only T'Pol has heard of this species, and she reveals that they are an aggressive, territorial race. Archer orders Hoshi to compose a response explaining the crew's desperate circumstances.

Out on the hull, Archer works painstakingly to de-activate the mine. He also tries to engage Reed in casual conversation, but it doesn't seem to calm the armory officer's nerves. Rattled, Reed reveals that he doesn't believe socializing with superior officers has any place on a starship. Archer, however, points out that the crewmembers all have to depend on one another, and that Enterprise's mission is not a typical one. As they continue to talk, it becomes apparent that Reed is prepared to sacrifice himself for the ship. Archer, however, is determined to save both his officer and Enterprise.

On the bridge, the crew is being hailed yet again by the Romulans, who insist that Enterprise leave. The Romulans know that Reed is trapped outside, but demand that the ship jettison the section of hull plating. Complicating things even further, the mine re-arms just as Archer believes he's defused it — he is forced to quickly re-set it again. Reed ascertains that they will now have to dismantle the entire mine, but there's no time. Reed once again volunteers to sacrifice himself, even going so far as to disconnect his air supply hose. Archer, however, won't have it, and quickly attaches the auxiliary air hose from his own suit to Reed's.

Desperate, Archer comes up with one last-ditch plan, and requests two shuttlepod hatches and a plasma torch. Trip detaches the section of hull plating, and, as they drift away, Archer uses the torch to free Reed from the hull. As the mine begins to arm itself, Archer and Reed grab their shuttlepod hatches and launch themselves out of harm's way. The mine explodes. As the Romulans descend on Enterprise, Archer and Reed make it back to the ship just in time for T'Pol to order the ship to warp speed. As Enterprise makes a safe getaway, Archer and Reed are left to ponder their ordeal.