Right from the opening seconds we know that something is seriously wrong with the Eastwood family.
Mother and daughter (Yvonne Mitchell and Sharon Gurney) scurry about surreptitiously, like prisoners, while husband / father Walter Eastwood (Michael Gough) dominates, lurks, and spies on them. Walter is an irredeemable pig. He's also violent. His son, Rupert (Simon Gough) is a chip off the old blockhead. A mere dinner at home is a maddeningly tense experience. Calling this family "dysfunctional", would be like calling the sun "warm".
It doesn't take long to see where this is heading.
CRUCIBLE OF HORROR is sort of a familial version of DIABOLIQUE, up until the jaw-dropping-ly impossible, ambiguous, yet perfect ending. Many questions arise, such as, "Was it all a dream / fantasy?", "Was there something afoot PRIOR to the vengeful scheme?", "Were supernatural forces at work?". Of course, this is all left open-ended, so, it's up for debate. Worth a watch. See if you can figure it out.
Michael Gough gives one of his best performances...