Hammer Films was known mostly for its horror outings like the Dracula, Frankenstein and Mummy films. It did, however, score well in the science fiction department with such hits as the Quatermass series, “The Lost Continent” and this movie.

The film was originally pitches as a potential sequel in the Quatermass series until author Nigel Kneale objected. Thus, the scientist became Alan Royston (played by Dean Jagger of “Twelve O’Clock High” fame) who worked at a nuclear plant instead of a rocket base and the location was moved to Scotland to avoid comparisons to Quatermass.

Ironically, the film still kept the same black & white photography, as well as the creepy string score.

The story involves radioactive mud (sounds silly unless you actually stayed awake during physical science class) that makes it way up to the surface of the earth every so often looking for new energy. Previous trips found nothing but fossil fuel. Now, however, nuclear energy is abundant. The race is on to not just figure out what is turning people into crispy critters, but how to stop something made of pure energy.

Dean Jagger as Royston is quite good and the exact opposite of Brian Donlevy’s Quatermass. Leo McKern (of “The Prisoner”) is on hand, as is the late British pop star and actor Anthony Newley as a soldier unfortunate enough to be on guard duty when X, the Unknown strikes.

The special effects are adequate, although British films still couldn’t show explosions that didn’t look like match heads flaring. The visual effects are really creepy, from radiation burns on a boy’s chest to a doctor’s face melting like wax to a security guard’s body literally deflating like a balloon. The ending features a surprise, as well, leaving the viewer with the feeling that, although man appears to have triumphed again, something may still be amiss.

All in all, a good film, especially late on a Saturday night.