6 Days a Sacrifice is a game in the Chzo Mythos series. It was the fourth and final game made, but the third chronologically. It is generally recommended that 6 Days be played last.
The game takes place 196 years after 5 Days a Stranger and 196 years before 7 Days a Skeptic. Theo DaCabe, a building inspector, is sent to inspect the headquarters of a new "religion", Optimology, after the police receive an anonymous tip about an unauthorized extension of the Optimology building. Once inside, a Mr. Garriott shoves him down an elevator shaft to imprison him. He is rescued by two escaped prisoners of the Optimologists: a shady biochemist, Dr. Samantha Harty; and an overenthusiastic journalist, Janine Orzechowski. Samantha soon informs Theo that Optimology is a cover-up and a money-making operation for the secretly operated Order of the Blessed Agonies, which seeks to bring Chzo into the Scientific Realm, the World of Technology. The building was built around the ruins of DeFoe Manor, which still houses John DeFoe's mind, even though his body is destroyed 196 years earlier and his soul is destroyed 196 years later.
With the help of a mysterious figure known only as the Caretaker, a barefooted bald man clothed in tattered blood-red robes, they are able to repeatedly escape capture by the Order. The three eventually open the "Hub", the chamber that contains the ruins of the DeFoe Manor, but, while exploring John DeFoe's mind, Samantha dies mysteriously from having her throat slit when she goes to explore the hub. Theo later deduces that Samantha once worked for the Order to help restrain John DeFoe's mind by perpetually cloning Trilby; DeFoe had become so fearful of Trilby that his mere presence was enough to keep the house stable and contained within the Hub. Theo, Janine, and a Trilby clone venture into the Hub, but Trilby is once again killed by the Prince, allowing for the entrance of John DeFoe. Theo and Janine escape to the sleeping quarters, where Janine, even more distressed by the recent events, makes love to Theo to receive comfort. She is possessed by DeFoe the next day, prompting her murder by the Prince. The Caretaker soon explains her dark possession: Theo's love for her tainted her with the darkness of his fate. Theo, now desperate to uncover the truth behind the madness, explores the Hub with a number of Trilby clone escorts who are continually killed by the Prince. He dons the apron, welding mask, and machete of John Defoe and enters a portal in the manor's kitchen. Theo explores strange visions (including one of the spaceship Mephistopheles explaining the hand reaching out of the locker in Dr. Somerset's dream in 7 Days a Skeptic). After these visions he finds himself in the DeFoe basement, where he discovers a "nanoexplosive" bomb powerful enough to destroy the entire Optimology building. Theo discovers that the bomb is disarmed; however, the manor is set ablaze by the last remaining Trilby clone when the Caretaker suggests that the manor is not burned down as it should be. The flaming petrol reaches and detonates the bomb, destroying the Hub, the manor containing DeFoe's mind, and allowing Chzo to bridge the Realms of Technology and Magick. In this incident, Theo suffers through terrible visions before his death.
However, instead of sending his own minions to the Scientific Realm, Chzo only brings Theo and the last surviving Trilby clone into the Ethereal Realm, the World of Magick, before the bridge closes once again. He transforms Theo, who has inadvertently become his acolyte as a result of the Blessed Agonies he has suffered: the Blessed Agony of the Body, due to his fall down the elevator shaft; the Blessed Agony of the Soul, due to the loss of Janine, whom he loved; and the Blessed Agony of the Mind, due to his traumatic experiences in the Order's complex and the visions before his apparent death. Chzo strips the Prince of his powers and grants them to the dying Theo, who becomes the New Prince. The New Prince easily defeats the former Prince (now called the Arrogant Man, his title before becoming the Prince in the Order's scriptures) and replaces him as Chzo's foremost servant. The Trilby clone is imprisoned and tortured by Chzo, who feeds on his agony.
In a cutaway segment, the Caretaker is revealed to be Malcolm Somerset, the protagonist of 7 Days a Skeptic, who murdered and impersonated his father Jonathan, and who has been convicted for the murders of all the people killed by DeFoe's spirit aboard the starship Mephistopheles. Somerset has been committed to an asylum for the criminally insane; however, he is given by the Caretaker — now revealed to have instructed Somerset to kill his father — a magical key-shaped knife once belonging to the Order's founder. This key opens a fleshy door in his cell (which represents the flesh of Somerset's throat), allowing him to descend an increasingly bloodied staircase, invoking flashbacks to the Mephistopheles where he sees the crew members deaths through John DeFoe's eyes; this is perhaps a metaphor for Somerset's suicide (his guards later find him dead in his cell). The mind and soul of an individual killed with Frehorn's Blade remain together after death, making the person's spirit immensely powerful but subject to the will of whoever wielded the Blade; Somerset has exploited a loophole in these rules by committing suicide with it and therefore remaining fully under his own control. He is transformed into a being of pure will, able to travel across time and between both realms. He enters Chzo's body to find the deteriorating clone of Trilby, captured after the explosion, who asks Somerset to kill him with Frehorn's Blade. Somerset does so and the Trilby-clone's life force is transferred to the real Trilby, who is about to die at the Clanbronwyn Hotel (this comes from the end of Trilby's Notes, where his survival was not explained). Travelling back to the complex, Somerset finally prompts the Trilby clone to set fire to the DeFoe Manor. Watching the destruction of the Optimology building, Somerset discloses in a final monologue that he is destiny's servant, and that his duty is only to make sure that time plays out as he foresees — now preparing to yet again prompt his young self to kill his father, setting forth the events occurring in 7 Days A Skeptic.