Professor Bernard Quatermass, Brian Donlevy, struggles to win government backing for his moon colonisation project, and his attention is drawn to reports of hundreds of meteorites falling in Winnerden Flats. Travelling there with Bryan Forbes, who plays Marsh, he discovers a vast complex already under construction, built around plans that echo his own lunar colony scheme. Marsh, eager to uncover the truth, examines an undamaged meteorite shaped like a small stone rocket. When it cracks open, a mysterious gas erupts, and Marsh is left with a strange V-shaped mark on his face. Uniformed guards, all bearing similar V-shaped signs, storm the area, subduing Marsh and shoving Quatermass away as he is knocked to the ground.
Seeking answers, Quatermass reaches out to Inspector Lomax, [John Longden], a police investigator who had helped him before. Lomax connects Quatermass with Vincent Broadhead, [Tom Chatto], a member of parliament determined to pierce the veil surrounding Winnerden Flats and the opaque project that supplies vast quantities of materials and manpower without any clear purpose being disclosed. Quatermass and Broadhead go on an official tour of the dome-dominated complex, which is described to be manufacturing synthetic food. Yet as they explore, Broadhead slips away from the party and manages to slip inside one of the towering domes. He is found later, dying and covered in a corrosive black slime, whispering a warning about what lies inside before he expires.
Back at the administrative level, Lomax and Quatermass attempt to alert higher authorities, but the corruption runs deep. When they confront the police commissioner, they discover the man is also marked with the same V-shaped symbol that has appeared on others under the aliens’ control, a sign that the extraterrestrials have infiltrated key government positions. The two men then recruit journalist Jimmy Hall, [Sid James], who is initially skeptical but curious enough to visit Winnerden Flats for a firsthand look.
A violent confrontation erupts at the community centre near the complex when a meteorite crash injures Sheila, the local barmaid played by [Vera Day]. The impact brings an alien presence into the village, and Hall is shot dead by the plant’s armed guards as he tries to phone in a report. A mob forms, and the villagers, alongside Quatermass and Lomax, push back against the guards and rush the gates, barricading themselves inside the pressure control room at the heart of the operation.
In a crucial tactical move, Quatermass deduces that Earth’s atmosphere is poisonous to the visitors. He executes a daring plan to sabotage the aliens’ life-support systems by flooding their domes with pure oxygen, slowly suffocating the creatures inside. Concurrently, Dr. Tom Brand, [William Franklyn], who works at the rocket complex, is gunned down by the intruding guards from Winnerden Flats, but not before he manages to launch an atomic rocket toward a nearby near-Earth asteroid that the aliens appear to use as a staging point. The explosion from the rocket devastates the asteroid, and the massive alien masses—each composed of countless smaller beings—burst from their domes in a 150-foot-tall surge.
As Earth’s atmosphere floods the domes, the giant masses collapse and the aliens die. The creatures’ influence over humans dissolves, and the V-shaped marks vanish from those who were touched by the invasion, leaving no memory of the control they once endured. With the immediate threat extinguished, Quatermass and Lomax make their cautious way back to the village, wondering how to frame a final report that will be believed, while contemplating how definitive any conclusion can truly be after such an encounter.
This tale blends scientific curiosity with political intrigue, showing how a single, unresolved mystery can ripple through science, government, and everyday life. It paints a portrait of a world where progress and secrecy collide, where a monocultural reliance on control is challenged by an unseen, intelligent presence, and where two determined investigators must weigh evidence, risk, and responsibility in the face of a truth that may be almost too vast to fully comprehend. The ending lingers with a sense of unsettled doubt, inviting viewers to ponder what, if anything, can be written into a definitive, final narrative about what happened at Winnerden Flats and beyond.
