**SPOILERS** For the first time in his life brilliant detective and world renowned criminologist William Sabastian, Robert Culp,is scared and unsure of himself in solving an unsolvable, for anyone else but him, crime a crime involving the supernatural. William had dabbled in the supernatural before and ended up almost losing his life. His heart was literally ripped out his chest but with the help of his faithful maid Lilith (Majel Barrett), who has a deep knowledge of occult practices, saved his life but William was left a very weak and frighten man.
Calling his friend Dr. Ham Hamilton, Gig Young, over to go with him on a case in the UK William feels that he'll need him if anything goes wrong in a case, of the bizarre and supernatural, he's investigating there involving the Cyon House headed by Sir Geoffery Coyn, James Villiers. Sir Geoffery's sister Anitra, Ann Bell,feels that there's strange and evil goings on in and around the Coyn Esatae and that her brother Geoffery is the cause of them and that her life is now in danger.
Willian and Dr. Hamilton arrive in London and go to see a friend of his, Quellious, at the Marlin's Mews but find the place on fire with Mr. Quellious dead viciously clawed by some unknown animal in the middle of a giant Pentagram that was on the floor. William knowing what the Pentagram stands for, The Devil's Sign, get's himself and Dr. Himilton to stand in the middle of it and thus prevent themselves from being burned alive. William also finds a journal on Quellious written in ancient Coptic that if deciphered explains what evil is really going on at the Coyn House and who's responsible for it.
Later at the Coyn House William and Dr. Hamilton meet the Coyn's including young Mitri ,John Hurt, a professional pilot who flew them to England from the USA. William senses that these's a strong presence of the Devil there but, besides the Coyn's also their staff of maids and male servants, who exactly is he or she? Using his skills as a top crime investigator William deduces that all this horror that struck the Coyn House centers at the Stonehenge-like site on the estate called the "Fire Pit". The "Fire Pit" was excavated by Sir. Geoffery some three years ago and since then all hell broke loose. Thats when these strange and weird events, that according to Anitra, began to happen. William also finds out that all the workmen who were part of that excavation mysteriously died.
Robert Culp as a modern Sherlock Holmes with his Dr. Watson-like friend Dr. Hamilton have their hands full in this suspense/thriller. With them stumbling upon the place where the Demon Asmodious, the Lord of Lechery, has his home-base the secretive " Hell Fire Club". It's there where those in power and high office, in both England as well as in the world, were members of.
Wild and fiery ending with the demon worshipers and their Idol Asmodious thrown back into the bottomless pit by a courageous and revived, back from his heart-ailment, William Sabastian during an orgy of sex and human sacrifices. The very graphic orgy sequence in the film must have been cut when "Specter", a made for TV movie, was first broadcast on NBC Television back in May 1977 but is in the cable TV version of the film.
