Captain Archer is eager to investigate the dark surface of a "rogue" planet — one that has broken out of its orbit. Due to hot gas venting from the planet's interior, small oases have formed, and scans show a surprisingly large number of varied life forms within them. Lieutenant Reed also picks up a power signature — apparently, there is an alien ship on the surface, but it is unresponsive to hail attempts.
Archer takes an away team consisting of T'Pol, Reed and Hoshi to the thick, black jungle of the planet's surface. Using their scanners and nightvision technology, the team locates an alien campsite. Archer sends T'Pol and Reed to check out the alien ship, while he and Hoshi stay at the campsite in case the aliens return. As Reed and T'Pol investigate, they are suddenly ambushed by two camouflaged alien hunters. The hunters, however, appear to realize that the two officers are not a threat, and take them back to the campsite. They return to find Archer and Hoshi getting along with the hunters' leader, a man named Damrus.
Over dinner, the team learns that these hunters, the Eska, have been coming to the planet to hunt for nine generations. Interested in learning more about their hunting technology, specifically how they managed to evade his sensors, Reed requests to join the Eska on one of their hunts in the morning. Although reluctant at first, Damrus relents and allows Reed to join them. Reed and Hoshi return to Enterprise to put together some camping gear, and Hoshi remains onboard while Trip takes her place on the planet. While everyone turns in for the night, Archer remains by the campfire to enjoy the fresh air and the stars, and soon falls asleep outside. He is awakened by a strangely familiar female voice calling his name from somewhere just outside the camp's perimeter. Hearing a soft rustling from within the jungle, Archer finds himself strangely drawn to the voice, and steps into the blackness to investigate. He finds nothing and quickly questions whether he imagined the voice, until he turns around to find a beautiful, oddly familiar woman mere feet from his side. She is almost glowing, bathed in an ethereal light. Unfortunately, as soon as Archer turns the harsh glow of his flashlight onto her, she vanishes into the jungle as though she were never there. Returning to the camp, Archer informs everyone of what happened, but the crew and the hunters seem to believe he imagined the incident.
The next day, Reed gears up to hunt with the Eska, while Archer, T'Pol and Trip head off to explore some nearby steam vents. During the hunt, Damrus and one of the other hunters, Burzaan, split off to check out something they call a "wraith," while Reed and the third hunter, Shiraht, continue into the jungle. Meanwhile, Archer spots the mysterious woman again, and follows her. This time, the woman speaks to him, asking for help. Before Archer can figure out what she means, Trip and T'Pol approach, frightening the mysterious woman away. When the three officers return to camp, they find the Eska tending to Burzaan, who was injured during the hunt. Archer offers to have Dr. Phlox take a look at Burzaan, and though Damrus is initially reluctant, he finally accepts Archer's assistance.
While Phlox tends to Burzaan, Archer returns to the oasis he visited earlier with T'Pol and Trip, hoping for another glimpse of the mysterious woman. She finally appears, and Archer learns that she is a telepathic shape-shifter, and that her kind is being hunted by the Eska for sport. They need Archer's help to survive. Enraged, Archer returns to camp to find his away team and the Eska — thanks to Dr. Phlox, Burzaan is healed. That night around the campfire, Archer plays coy in order to gain more information from the Eska. The hunters admit that the prey they've been hunting are shape-shifters — the Eska call them "wraiths." The Eska also admit that they have learned how to take advantage in the hunt: the wraiths emit a chemical signature when they're afraid, and the Eska scanners have been modified to detect that signature. Returning to Enterprise, Archer shares his outrage with the crew, and asks Dr. Phlox if there's a way to mask the wraiths' chemical signatures, shielding them from the hunters' scans. As he has a wraith cell sample taken from Burzaan's wounds, Phlox believes he can find a way. While he's waiting for the results, Archer discusses his mysterious woman with Trip. He brings up a Yeats poem his mother used to read to him, about a man who catches a fish that turns into a beautiful woman, then disappears. The man spends the rest of his life searching for the woman, for his vision of perfection, but never finds her. Archer believes the woman is his own visualization of the woman from the poem. As he thinks about this some more, Archer is informed that Dr. Phlox has made progress.
Later, the Eska pursue a wraith down on the planet. As they corner it, the hunters start firing on the wraith in order to scare it into releasing its telltale chemical. Nothing happens, and then the wraith escapes, melting into the jungle. Realizing they no longer have the upper hand, the beaten hunters return to their ship and leave the planet's surface. When they're gone, Archer has a final conversation with the mysterious woman, who thanks him for the masking agent. Archer wonders why she chose to appear to him as the woman from the poem. She simply smiles, bids him farewell, and reminds him to never stop seeking what seems unattainable.