The Sorcerers is a 1967 horror film directed by Michael Reeves and starring Boris Karloff. It's good to see Karloff in the 1960's. This is an interesting film. Catherine Lacey plays Karloff's wife and is fascinating in the role. She does a great evil.
Embedding is disabled on most of the pieces, but this film is available on youtube divided up into sections: part 1, part 2, part 3, part 4, part 5, part 6, part 7, part 8
DVDTalk praises it, but reviews are hard to come by.