Archer enters the Situation Room for the briefing at the start of the shift. T'Pol reports several interesting phenomena; the remnants of a J'ral-class nebula or a cluster of three neutron stars. Archer looks unimpressed. Trip says that there is a third option, a Minshara-class planet with 500 million bio-signs, 78 light-years from Earth. The senior officers laugh at Archer's pleased expression. He turns to T'Pol and says; "You might have put that at the top of your list". T'Pol is impassive.
The Enterprise orbits the planet at 500 kilometres. T'Pol doesn't detect any EM transmissions, making Trip think that it is a preindustrial culture. Hoshi zooms in on a port to see a clipper ship making for harbour. T'Pol recommends against visiting the surface, as Vulcans wait until a society has developed warp drive before making First Contact. Enterprise can gather survey data with its sensors instead. Archer asks Hoshi to zoom in on two of the Akaalians. They have a strong resemblance to humans. Archer says that Starfleet sent the Enterprise on its mission so that the human crew could explore with their senses, not just use the ship's equipment.
Later, Hoshi uses the acoustic relay to listen in on dozens of languages; the Universal Translator will take time to determine a translation matrix for them all. In the Ready Room, T'Pol recommends landing on a remote, sparsely-populated farm to reduce the risk of cultural contamination if they are exposed as aliens. Archer jokes that it must be the reason why aliens always land in cornfields on Earth.
In Sickbay, Phlox finishes his cosmetic modifications on the first of the landing party. He hands Hoshi a mirror to examine his handiwork. T'Pol summons Archer to the Bridge. He and Hoshi arrive to hear T'Pol report that she is detecting neutrino emissions from a city on the eastern continent, possibly caused by an anti-matter reactor. Archer thinks that they are not the first explorers to visit; T'Pol doesn't detect any non-indigenous bio-signs. Archer orders Trip and T'Pol to accompany him to Sickbay and asks Hoshi to tell the Quartermaster to prepare three more sets of Akaalian clothing.
In the shuttlepod, Hoshi hands out papers for the landing party; everyone in the city for which they are headed has to carry a set. T'Pol has long, dark hair to cover her ears. Trip reminds her to brush it forwards when it slips back. The shuttlepod lands at night in a grove near the city.
The landing party wander through the city, which appears to be similar to the European Middle Ages. Hoshi and T'Pol move to a quiet alley in order to scan the area. Hoshi stands on watch and meets an Akaalian's gaze; he moves off quickly to his female companion. They both have mottled skin and appear sick. Later, Trip and Archer find a signal on their tricorders and move towards a building to investigate. The reactor is eight metres under a curio shop which is locked for the night. Trip produces a device and sets to work on the lock. The pair are observed from the shadows by a cloaked figure.
Archer sees the shadow of an approaching Akaalian and warns Trip, who opens the lock in time. They enter and the Akaalian passes by. Archer signals to T'Pol that they have found the generator; T'Pol agrees to meet at their coordinates.
As they move to the rear of the shop, the front door opens and the cloaked figure enters, revelaing her face in the moonlight. She watches as Archer encounters a forcefield in front of the door to the room containing the reactor. Archer and Trip turn as they hear a sound. The woman, Riann, has produced a small crossbow and points it at them. Archer claims that they are collectors, at the shop to collect an antique. Riann doesn't believe them. She says that she has been watching the shop for weeks, observing evening deliveries. She is doing so because people are getting sick, some even dying because of the shop. As they move away from the door, T'Pol stuns Riann with her phase pistol. Hoshi reads the Riann's papers and finds that she is an apothecary. Archer tells the landing party that he will meet them back at the shuttlepod.
Later, Riann awakens in her apartment. She asks if Garos, the shop's owner, told Archer to bring her back. Archer pleads ignorance and claims to be an investigator from another city, trying to find out what is going on in the shop. Archer agrees to meet Riann in her apartment the next day to talk about the sickness. He tells her his name, Jon, before leaving.
Archer communicates with Reed, who says that the energy field would stand up to a barrage of torpedo fire. Reed can't detect anything under the shop, no basement area or bedrock. Trip thinks that a damping field must be present. Phlox may be able to diagnose the sickness but T'Pol advises against bringing an Akaalian back to the Enterprise due to cultural fears of alien abduction. She recommends talking to Garos first.
In the shop, Archer and Trip pose as amateur antiques collectors. Garos shows Trip a mask of Draylan, the mythical ruler of the afterworld. Trip doesn't recognise it, making Garos curious. Archer uses the distraction to scan the shop with his tricorder, then tells Garos that his DNA doesn't match any Akaalian lifeform. Garos pulls out his own scanner and says the same to Archer.
Archer explains their presence and Garos claims never to have heard of Earth. Garos explains that he is from the Malurian System and used to be an explorer too. He was part of a survey mission to study the Akaali but found himself taken with the people after a few months and decided to stay. Archer tells Garos about the illness and Garos sees Riann's handiwork. Garos says that the illness is an indigenous virus and the Akaali don't have the medical technology to cure it. A new customer enters and Archer and Trip leave. Archer summons T'Pol to Riann's apartment.
T'Pol scans Riann's laboratory while Riann works at a microscope. Archer tells Riann that Garos has a machine in his basement that may be connected to the epidemic. Riann learned of the epidemic 18 months ago; her brother was one of the first victims. The illness never spreads beyond the part of the city where Garos' shop is located. Riann shows Archer a map plotting the cases of the illness, all within the vicinity of the shop. Riann goes on by saying that Garos produces crates of goods from his shop for distribution outside the city every few days. T'Pol leaves to begin her analysis of the information that she has collected.
Back on the Enterprise, Phlox is impressed with Riann's forensic techniques. Phlox analyses the water sample that T'Pol collected. It is contaminated with tetracyanite 622, a synthetic compound used as an industrial lubricant and quite toxic. Phlox thinks that it could be responsible for the epidemic.
That evening, Archer and Riann watch the shop from the cover of some stairs, Riann writes in her journal. As she speaks, the Universal Translator malfunctions. To cover his lack of understanding, Archer kisses Riann passionately to cover his fiddling with his communicator. They see a man leave the shop with three crates that he proceeds to load on to a handcart.
They follow him to a clearing in the woods where he unloads the crates before speaking an alien language in to a communicator. He leaves and they approach the crates but before they can open one a powerful light illuminates them. They escape and see a shuttlepod descend, its cargo bay doors opening to use a tractor beam to lift the crates. Riann is amazed. They are interrupted by phaser fire. Archer pulls out his phase pistol and goes to investigate. He finds the shooter and overpowers him. Bending over the figure, Archer pulls at his face to reveal it to be a mask, with a reptilian face underneath. Archer reaches his pistol first and stuns the Malurian. Riann is horrified when she sees. Archer is forced to tell the truth.
Archer and Riann go to the shop. Archer has a control device for the forcefield, which he deactivates. They enter the basement and find the generator. On a viewing platform, they see that the shop has a large cavern beneath it, housing platforms and industrial plant, staffed by a contingent of Malurians.
Archer radios to T'Pol on the Enterprise that Garos is mining a kind of veridium isotope. T'Pol says that its primary use is in the manufacture of explosives. The tetracyanate saturates the drill bits, polluting the local water table. Archer concludes that he will try to deactivate the damping field to enable the use of the transporter for the reactor. Riann and Archer find a control panel that appears to control the damping field. There are two buttons, blue and yellow. Archer chooses the blue button as it is illuminated. An alarm sounds and the doors close automatically.
The Enterprise detects a ship approaching, heavily armed. Garon hails from the surface, suggesting that the Enterprise depart at once. Garon says that Archer is dead and the ship opens fire as a warning shot. In the basement, Garon appears behind a glass panel and asks Archer how he learned about the facility - from an ugly Tellurite merchant? Garon says that a few thousand Akaali won't be missed from a population of 500 million, justifying continuing his mining operation. Garon lies when he says that he asked T'Pol to send a shuttlepod to collect Archer and Riann. Archer gives Riann the phase pistol and tells her to shoot anyone who enters the room.
In orbit, the Enterprise is tracked by the Malurian vessel. T'Pol orders Mayweather to prepare to leave orbit. Trip protests and T'Pol says that she will not abandon Archer, dead or alive. Back in the basement, Archer succeeds in deactivating the damping field, opening the locked doors. Reed locks on to the generator and the Malurian vessel fires again. T'Pol orders evasive maneuveurs. Archer and Riann walk casually through the crowded street. Garon appears behind them, searching up and down. Onboard, T'Pol says that if the Malurians want their reactor so badly, perhaps the Enterprise should give it to them.
In the street, a Malurian sees Archer and Riann, pulls out a phaser and fires, scattering the crowd. Archer stuns the first Malurian and pulls Riann in to cover as Garon and his accomplice open fire from further up the street. The crowd escapes in a panic.
In orbit, Trip locks on to the generator with a transporter beam, while Reed loads a torpedo tube. T'Pol orders Trip to energise and he puts the generator midway between the Enterprise and the Malurian vessel. Reed fires the torpedo at the generator and the resulting explosion drops the Malurian shields. T'Pol orders the ship to come about and target their weapons array.
In the street, Riann spots an oil lamp behind Garon. She tells Archer that the oil will ignite if heated to 398 degrees. Archer resets his phase pistol and destroys the lamp, stunning Garon and his accomplice. T'Pol asks if Archer wants the Malurian vessel disabled. He replies no, as they need to take Garon away. Garon reaches for his scanning device and activates a transporter beam, removing all three Malurians.
Archer visits the surface for a final time. He gives Riann medicine for the sick. The Vulcans will scan the planet from time to time to ensure that the Malurians don't return. Archer kisses Riann goodbye. She asks if his translator is broken again. Archer smiles and says that he doesn't understand her before smiling and resuming the kiss.