As Father Brennan presses Father Harris regarding a sinister conspiracy, Harris's anxiety escalates dramatically. In a moment of desperation, he hands Brennan a haunting photo of a newborn, ominously labeled "Scianna." Tragedy soon befalls them when Harris's life is brutally cut short by a falling pipe, a shocking event that shatters not only his skull but the fabric of their inquiry.
Set against the riotous backdrop of 1971 Rome and its left-wing protests, American novitiate Margaret Daino arrives at the Vizzardeli Orphanage. There, she encounters notable figures such as Cardinal Lawrence, Father Gabriel, and the Abess Sister Silva, alongside nun Anjelica and her roommate Luz. As Margaret adjusts to her new environment, she becomes increasingly drawn to Carlita, a mistreated orphan haunted by unsettling visions, amplifying the dark atmosphere enveloping the orphanage.
As tensions rise, Brennan forewarns Margaret about Carlita, ominously predicting that "evil things" will soon revolve around this fragile child. Within this foreboding context, Margaret uncovers a disturbing drawing of a pregnant woman bound and soon bears witness to Anjelica’s horrific self-immolation, a calamity that sends shockwaves through her psyche.
Brennan then unveils a chilling reality: radical elements within the Church are conspiring to resurrect the Antichrist, intending to exploit Carlita to fulfill their dark prophecy. Amid a chaotic field trip, Margaret's grasp on reality begins to erode as she finds herself beset by terrifying demonic hallucinations. In response, Sister Silva postpones Margaret's vows, insisting she distance herself from Carlita. However, Margaret is deeply shaken by the tragic death of Paolo, who cryptically implores her to "look for the mark" before he meets his own grim fate.
In her pursuit of the truth, Margaret infiltrates Sister Silva’s office, discovering a hidden underground chamber replete with files labeled "Scianna." These files contain photographs of malformed newborns, each bearing a troubling birthmark shaped like three sixes, with Carlita appearing to be the only survivor. As she digs further into this nefarious enigma, Margaret is caught and forced to confront the mark on Carlita's palate before finding herself imprisoned.
A daring rescue is mounted by Father Gabriel, who liberates Margaret, allowing her to join Brennan in examining the disturbing files. Together, they unveil a shocking truth: another child had survived, drawing Margaret unwittingly into a malevolent game tied to a larger satanic ritual. As she discovers a mark on her own scalp, harrowing memories surface from the fateful night at the disco, leading her to the horrific realization that she was violated by the Devil himself, placing the Antichrist's conception perilously at stake.
Upon regaining consciousness, Margaret finds herself restrained to a sterile hospital bed, surrounded by the foreboding figures of Cardinal Lawrence and his ominous associates. The atmosphere is thick with dread as they witness the birth of not just one, but two infants—a boy and girl—whose lives are irrevocably connected by the celestial circumstances of their arrival. Amid the turmoil of childbirth, it becomes chillingly apparent that the infant boy is marked for notoriety as the Antichrist, his malevolent essence evident even in the early days of life.
As the narrative unfolds, Luz and a mysterious figure linked to Paolo at the disco are unveiled as conspirators, their deception intricately woven into the story. Pretending to comply, Margaret asks to cradle her newborn son, seizing the moment to strike back against Cardinal Lawrence, her blade finding its target with deadly precision. Yet, the struggle to rid herself of this demonic entity within her own child confounds Margaret, as she grapples with the instinct to protect her flesh and blood.
In the ensuing chaos, Luz viciously turns on Margaret, accurately hitting her mark as the conspirators make their escape, leaving behind a trail of destruction that threatens to engulf them. In the flicker of flames, the angelic figure of Carlita emerges, rescuing Margaret and her daughter from near certain doom. As they flee into the dark night, Margaret catches a fleeting vision of a demonic jackal amidst the flames—an image destined to haunt her for a long time.
Thus, as the dust settles over this apocalyptic tableau, a new chapter reveals itself. The baby boy, now referred to as Damien, is spirited away by American diplomat Robert Thorn, leaving his unsuspecting wife Katherine in blissful ignorance. Their once-innocent lives become entwined with the sinister forces poised to claim Damien's soul, propelling Margaret and her daughter into a perilous life on the run, forever connected to an unimaginable dark destiny.
