“Burn, witch… burn!”

For much of its running time Night Of The Eagle is all about shadows and unanswered questions. But when it veers into out-and-out horror, it's terrifying.

It is also beautifully crafted - one of those films that needs to be watched several times to take it all in. As we're introduced to the lives of Professor Norman Taylor (Peter Wyngarde) and his wife Tansy, the camera lingers on a number of seemingly innocuous items - all of which will take on a more sinister air later on.

Norman is introduced to us during a lecture on witchcraft, scribbling these fateful words onto a blackboard: "I do not believe!" (with the "not" underlined).

"Four words necessary to destroy the focus of the supernatural," he explains to his students. "Belief is vital!"

Norman and Tansy seem to live a charmed life - he's loved by his students, he has a good job and is on the crest of a wave - even though he's disliked within the college itself (mainly by the jealous wives of his peers). When, at their Friday night bridge rubber, his friend lightheartedly accuses him of "selling his soul to the devil" for his "charmed life", Tansy reacts badly.

Back home, Tansy seems worried and starts searching for something. Norman finds a dead spider in her underwear drawer, and realises it "means something". A search of the house the next day leads to the discovery of a whole host of strange totems and charms, which he piles onto the kitchen table and waits for Tansy's return.

His questions are soon answered: "Isn't it obvious? I'm a witch!"

She's been practising spells taught to her by the witch doctor Corubius during a recent stay in the Caribbean.

An incredulous Norman, who has built a career out of poo-pooing such things, makes Tansy burn all the charms, despite her protestations that she believes dark forces within the faculty are threatening to destroy him, Norman seemingly joking when he replies: "If we were to investigate the strange rituals performed by women on their intuition, half the women in the country would be in an asylum…"

Unfortunately, the dolt also chucks his own photo onto the fire (much to Tansy's horror) - and instantly gets a breathless phone call from a very suggestive woman.

Suddenly, everything takes on a much more sinister edge and the whole film lurches into spooky territory. Norman narrowly avoids a speeding van, a female student brings a charge of rape (or "violating her" as the charming 60s vernacular puts it), and her boyfriend threatens him with a gun.

Yet still Norman refuses to believe that all this has anything to do with the previous night's pyrotechnics. He deals with the rape charge quickly and efficiently, through the power of shouting: "You phoned me on Saturday night, with a very disgusting proposition!" he sensitively tells the crying girl. "When I threatened to hang up, you used vile language - VILE AND FILTHY!"

"I had to call you," the distraught girl replies. "I don't know what came over me…"

So that's that cleared up, then.

The whole gun thing is also cleared up with a quick slap.

But the "forces of darkness" don't stop there. A tape of one of Norman's old lectures arrives in the post, with a strange noise overlayed on the top of it. The phone rings, and the peculiar droning can also be heard on the other end of the line. Suddenly an otherworldly screeching comes from outside, but the noises stop before whatever it is can be seen.

"I'm not going to say that there was something out there, Norman," says a by-now-quite-hysterical Tansy, "that is what you want me to say!"

As Norman sleeps, Tansy prays to be allowed to die in his place (what a wife!), and the next morning she's disappeared, leaving a taped message:

"It's the only way to defeat the horror that threatened to destroy you last night. I have gone away so this terrible curse can no longer touch you. There is nothing you can do Norman, nothing. I do love you. I love you."

Realising she's probably going to their seaside holiday home, Norman follows in his cool sports car. Attempting to attract her attention as she dozes on a bus, he has a near miss with a truck and wrecks his car - finally arriving at the cottage after darkness has fallen. Tansy isn't there, or in the nearby cemetery (but Norman does walk straight past her on the beach without noticing - another brilliantly spooky scene).

Showing that he's beginning to believe, Norman erects a makeshift shrine in a crypt ("The house of the dead, in the place of the dead") in an attempt to save Tansy (who we see walking out to sea, Reggie Perrin- style).

As Norman brushes away the shrine, thinking he's failed, Tansy appears, sopping wet, in the doorway of the crypt. He takes the now-catatonic woman home, where she immediately attacks him with a knife.

Fighting her off, Norman realises she's limping - exactly like one of the women working at the faculty.

Going back to the college to confront the other witch, he finds out the truth - that there's more than one witch working in the college…

"You're behaving like a frightened schoolboy Norman," she tells him. "Frightened of being wrong - and you are wrong!"

"Burn, witch… burn!" she adds, setting fire to a pile of tarot cards - and across the quad, Norman and Tansy's cottage, with Tansy inside, bursts into flame.

Norman rushes to help, but the spooky tape is now played over the tannoy, and out in the open he's an easy target for the full-on demonic forces.

Norman, being pursued by a seemingly unstoppable demon and by now a gibbering wreck, stumbles into the classroom where we were first introduced to him. He staggers backwards into the blackboard, his shoulder rubbing off part of the message written there, and changing its meaning completely. Now written there, in his own hand, it simply says:

"I do believe."