In a close future, the nuclear war has eradicated all the vegetation on the Earth. While waiting for the end of the radiation's effects and for the atmosphere to become suitable to allow again the implant of animals and vegetables species on earth, specimens of each of them have been safeguarded and sent onboard huge Geodesic domes hung to spaceships.
The "Valley Forge" belongs to this three ships fleet, kind of a Noah's Ark from which depends the revival of our planet. On board, three technicians, Wolf, Barker and Keenan and a botanist, Lowell Freeman, who, a nature lover, exerts his job with passion. A passion manifestly not shared by the three other men who are only accomplishing a simple mission waiting for their money. Furthermore, the crew is seconded by a trio of small technician droids that intervene directly in all point of the ship.
But one day, the program is discontinued, the order is received to destroy the greenhouses. Collapsed, Lowell attempts to convince his team-mates that all this is an aberration and that it is not wise to obey. Theses greenhouses represent life, the only reason to exist for man. But all Lowell's determination to convince the three technicians does not change anything, they are decided to execute the orders.
While the "Berkshire" - one of the vessel of the fleet - begins to drop its spheres in space and to procees to their disintegration thanks to mini nuclear bombs, Lowell spends the few time left it remains to him in his greenhouse. Suddenly, Lowell acts. Unable to let this slaught proceed without doing anything, he fights to death with one of the technician. Lowell is gravely injured. Following his idea, he drops the dome where the two other astronauts still work and burst it out.
While Neal, the commander of the "Berkshire" hurries the "Valley Forge" to execute its mission, Lowell gives new coordinates to his spaceship, projecting it towards Saturn. He explains that the vessel is out of order and drifting inexorably to the planet. The "Berkshire" no longer can help Lowell and his crew. Losing a lot of blood and unable to keep his tourniquet anymore, Lowell programs the droid N°1 and loads a medical program in it in order that this one could surgicaly intervene on the botanist.
The new coordinates of the ship passes very close of the Saturn's ring. The "Valley Forge" is victim of fleeting turbulences that provokes the loss of the robot N°3. Alone in the vessel, Lowell renames the two other drones, Huey and Dewey and programs them to give him assistance with the maintenance of the greenhouse. Lowell makes new friends out of them.
One morning, Freeman notices that the forest is sick. In the hurry, Lowell strikes Huey with his internal displacement vehicle. He receives a unexpected message from the "Berkshire"...
Spoiler ! the end of the story is revealed below…
This one has succedeed in retreaving the trace of the "Valley Forge" and flies to Lowell's help that it should reach in six hours. Having not other choice, Lowell puts his last plan to execution. He comes to understand that the forest was in lack of light, leading to its wither. Unable to do anything more, he installs powerful projectors in the greenhouse to replace the action of the sun then he gives the dome of glass to Dewey's care. Lowell ejects the greenhouse and the little robot in space. He now prepares the self-destruction of the vessel that he explodes in desperation, while ahead, Dewey attends to the forest that resumes life.
No real happy end for this film realised in 1972, in the middle of the ecologist period and Hippie movement. It's besides Joan Baez who interprets the songs of the film. A sci-fi movie whose main message is the respect of the nature and the environment; so rare to be noticed.