An old Earth probe, Friendship One, approaches a Delta Quadrant planet, to the puzzlement of that planet's astronomers.
USS Voyager is assigned its first mission by Starfleet since becoming stranded in the Delta quadrant in the year 2371. Captain Janeway informs the crew that they have been assigned to find an ancient Earth probe launched several years after Earth's first warp flight. The probe, named Friendship One carried information on technology, such as antimatter reactors and communication transceivers.
After doing calculations to avoid such things as stellar drift, Harry Kim suggests skipping to the most likely place. They discover the probe is presently on a planet undergoing a nuclear winter. The Delta Flyer is sent down to investigate and retrieve the probe; however, after searching and finding a part of the probe, several humanoids ambush and kidnap Tom Paris, Neelix, and Lt. Joe Carey.
Chakotay and Harry return to the Delta Flyer, where Chakotay discovers that someone has tampered with the systems. While removing his spacesuit in the cargo bay, Harry is attacked, but Chakotay enters and stuns the assailant with his phaser. As the Delta Flyer shakes, Harry and Chakotay return to the cockpit and discover they are being attacked with anti-matter weapons, and that shields have failed. Chakotay takes the Delta Flyer up, stating that they will return for Tom, Neelix, and Carey.
Back on Voyager, Janeway and Chakotay talk and enter the sickbay where the Doctor awakens the humanoid they stunned on the planet. Janeway and the humanoid talk and exchange history, as the humanoid explains the technology brought by the probe sparked the nuclear winter on his planet.
The planet hails the starship Voyager, and Janeway and a man named Verin communicate. Verin demands that Voyager remove his people from the planet. He prepares to send a hostage through in return for food and supplies; however, moments before he is beamed away, Verin apologizes and kills Carey. His is the final crew fatality of the series.
As it turns out, Verin and all his people despise the humans because they blame them for their current dilemma, namely a planet wide disaster which arose from Verin's people applying the knowledge they garnered from the Human Friendship One probe.
Using her nanoprobes, Seven of Nine reveals to Otrin, a male they captured from the planet, that the first phase of his treatment is complete.
Voyager sends down the Delta Flyer with several officers. Tuvok is captured by the planet's natives and is brought to the caves, where the others are being held. Upon entering, his escort fires his weapon. Rendering the captors unconscious, Tuvok's escort removes his head cover, revealing himself to be the Doctor. As Tom Paris, Neelix, Tuvok and The Doctor prepare to beam out, Tom decides to bring along the child they helped save to Voyager, where he can receive medical care from their Doctor.
Otrin along with Seven show their invention to Janeway, a solution to correcting the planet's atmosphere. They consider using photon torpedoes to cause a chain reaction, applying their idea on a planetary scale.
As Voyager hails Otrin, notifying him that they are ready to begin, he wishes them good luck. When Voyager begins firing the modified photon torpedoes, the shockwaves of the explosions cause Verin to become paranoid, and proceeds to activate the planets defenses; however, the people of the planet stop him.
A young child enters the caves telling everybody to hurry outside. Once outside, they discover that winter has disappeared. The sun has come out and the young girl says itâs beautiful.