During a routine construction project in London’s Hobbs End, workers uncover a peculiar skull and mysterious metallic object buried deep underground. Authorities initially believe the discovery to be an unexploded World War II bomb, but upon further investigation by Dr. Roney, a paleontologist, the skull is identified as a primitive humanoid, suggesting a link to early human ancestors. As the dig continues, Professor Bernard Quatermass, a brilliant scientist, becomes involved, recognizing that the "bomb" is actually an ancient spacecraft of extraterrestrial origin.

Quatermass, along with Roney and his colleague Barbara Judd, uncover disturbing evidence that the craft has been buried for millions of years. The spacecraft, belonging to an advanced alien race, reveals strange powers, including telekinesis and the ability to evoke violent, primal memories in those nearby. As Quatermass delves deeper into the mystery, he uncovers a shocking revelation about humanity’s origins and the true nature of the beings that once inhabited the craft. The remaining half of the movie explores the terrifying implications of their discovery as Quatermass races against time to prevent a catastrophe.