Silent Running takes place sometime in Earth’s near future where all plant’s and forests have been destroyed. The government has preserved some of the remaining specimens of flora and fauna, and sent them into space.
Freeman Lowell is a forest ranger aboard the Valley Forge, a special American Airlines greenhouse/freighter about 2,000 meters in length. At this time, it, along with seven other identical ships, orbits to the rings of Saturn.
Lowell is completely dedicated to preserving these interstellar forests with hopes of eventually returning them to Earth for reforestation of the now-barren planet. However, his three shipmates, John Keenan, Marty Barker, and Andy Wolf, could careless about Earth’s environment. Technology has evolved to the point that the world’s temperature is a constant 75 degrees, all hunger and disease is gone, and everyone has a job. The planet is just fine as is, and the men only want to return home to it after being in cooped up in space for the last year.
One fateful communication from Earth orders all eight ships to destroy their six domes containing their forests, and return home to Earth so the freighters can be redeployed to commercial service. However, Lowell has dedicated the last eight years of his life to the project, and he fully believes in restoring the planet’s destroyed environment, so he disobeys orders.
The other crew members on the Valley Forge destroy four of their six greenhouses before Lowell snaps. Keenan enters the dome where Lowell is tending to the forest, and he tries to set the nuclear explosive. Lowell kills him instead, but he severely cuts his leg in the scuffle. He then traps Barker and Wolf in the other dome as they are setting its explosive device, and jettisons if from the ship as its nuclear bomb detonates; killing those men.
That leaves Lowell alone on the ship except for his three drone robots. He has them help him fake a premature detonation of the last dome to make his ship look disabled. This fools his superiors aboard the Berkshire after which he changes the course of the Valley Forge so it drifts through the Rings of Saturn. He then reprograms the drones to repair and stitch up his injured leg.
At this point, Lowell is still in contact with the rest of the fleet, and they let him know that he’s on a collision course with Saturn’s rings. There isn’t anything he or they can do to stop that, and the result of the collision will most likely be total destruction of the ship. They recommend he think about suicide.
The Valley Forge soon loses contact with the rest of the fleet, and it quietly passes through the rings. The three drones are outside the ship busily maintaining it. Drone Number Three is knocked off it; leaving just two remaining. However, the ship, along with its last remaining greenhouse dome, emerges undamaged on the other side.
With the help of the two remaining drones, Lowell charts a course for deep space. Alone and wanting some companionship, Lowell reprograms the drones and renames them Huey, Dewey, and the destroyed one, Louie. He teaches them to play poker and properly plant trees. Then he has them bury poor Keenan who’s been lying there dead for quite sometime now.
Unfortunately, despite all his valiant efforts, Lowell find his last forest dying for unknown reasons. As he speeds down the ship’s tunnel to the forest in a little buggy, he accidentally runs into Huey. The collision nearly destroys him. He does his best to repair the fella, but he isn’t completely successful although he does the best he can. The forest continues to die, and it looks like Lowell will not be able to save it.
Weeks pass before Lowell hears a human voice again when his radio crackles to life. The Berkshire has found the Valley Forge after an extensive search, and it’s on course to rescue it and Lowell. They tell him that they will reach him within six hours, and he should jettison his last dome, but not to detonate its nuclear charge as it’s too dark to safely do it.
Suddenly, Lowell realizes his forest was dying because of a lack of sunlight. He quickly sets up a group of bulbs in the dome to simulate that light. Then he instructs Dewey to maintain the forest as his last instruction to him. He and Huey then head back to the main portion of the ship.
Lowell knows when the Berkshire arrives, they will uncover his killings of his crew mates, so he jettisons the last dome to the uncertainty of space.
The Berkshire is now about two hours away from docking with the Valley Forge. We find Lowell sitting with a damaged Huey; arming the last of the his nuclear charges. As he prepares to destroy himself and the ship, he says to Huey, “When I was a kid, I put a note into a bottle, and it had my name and address on it. And then I threw the bottle into the ocean. And I never knew if anyone ever found it.”
The camera zooms out of the Valley Forge, and Lowell destroys it all.
The film ends with the now well-lit greenhouse drifting away in space. Dewey tends to the plants with a child’s battered watering can. Joan Baez’s sings us out to the film’s somber theme song.