Robert Manning (Mark Eden) is an antiques dealer who has just received a selection of rarities from his brother, Peter, after he visited an old mansion, Claxted Lodge. However, Peter hasn't been in contact for days, and Manning grows suspicious when the note that came with the rarities simply says that Peter hasn't been feeling well. Manning makes up his mind to get to the source of this mystery and heads off to the village of Greymarsh where the mansion is situated; stopping off to buy petrol, he asks the attendant about the village and is told they are holding a festival celebrating a witch burning from centuries before. Intrigued, Manning drives on...
Supposedly inspired by H.P. Lovecraft, Curse of the Crimson Altar is one of those horror movies you wish was better than it was - all it needed was a tighter, more imaginative script (the one they got was written by Mervyn Haisman, Gerry Levy and Henry Lincoln) and it might have flown. The reason you want it to be better is because it features a cast of fright film veterans, including Boris Karloff in his last completed role, but the story here doesn't even offer us the novelty of seeing them all in one scene together. Indeed, Barbara Steele, playing the green skinned witch Lavinia, seems to have shot her scenes in an afternoon at a location away from the rest of the cast, never meeting the others at all.
The mystery, too, is lacking as we see from the opening that Peter has become caught up with a witches' cult where he has committed human sacrifice. Why has he done this? We never really find out, in fact we never find out anything much about him. The hero is Manning, who when approaching the mansion catches sight of a young woman running towards him and screaming, pursued by some cars. Trying to be gallant, Manning leaps out to save her, only to be let in on the joke: there's a party going on and this was part of the festivities. We know what level of debauchery is happening as we see rampant body painting and champagne spilling going on up at the house.
Finding a quiet room, Manning meets Morley (Christopher Lee), the current owner whose niece, Eve (Virginia Wetherell), is hosting the party. As he said on the phone, Morley has no memory of Peter arriving, but offers to let Manning stay the night as local accomodation is poor. He also meets Professor Marsh (Karloff), who seems preoccupied with brandy and makes a study of witchcraft for a book he's writing, assisted by Eve. Manning takes quite a shine to Eve, forcing her into passionate embraces at every opportunity despite having a girlfriend back home which might enhance the manliness of his character, but lends him no benefits sympathy-wise.
One aspect that is successful is that we're not sure who is a baddie and who is a goodie: any one of the people Manning meets could be the villain, including the stuttering butler Elder (Michael Gough, another horror star making an appearance). But as we think that they're all in on the act, the suspense only relies on how long it will take Manning to work out what's going on - until the end of the movie as it turns out. All the while he has bad dreams of Lavinia demanding he give his soul over to her and the plot thickens until the revelation bursts on the screen without much warning. It was all to do with hypnotism, apparently. While the house is a top quality venue for supernatural events, the fine cast get little to work with, and Curse of the Crimson Altar looks very tame. Music by Peter Knight.