As the year 1955 unfolds, seasoned newspaper journalist Budiman Syailendra receives an urgent summons to witness an enigmatic occurrence at Bosscha Observatory. His steadfast ally, Heru, a police commander, has been burdened with the task of managing a chilling discovery — a multitude of exhumed corpses lies in front of a framed portrait of the mysterious Mawaran, as if paying homage. With strict orders to keep this unnerving revelation under wraps in order to preserve the country's reputation ahead of the significant Bandung Conference, Heru persuades Budiman to share the story through unconventional means, feeling deep down that the truth deserves to be revealed.
Fast-forward to 1984, where we find ourselves amid the dilapidated surroundings of Mandara Apartments in Jakarta. Rini has been struggling to make ends meet alongside her brothers Toni and Bondi, while their father Bahri Suwono remains shrouded in mystery, juggling odd jobs during the day while safeguarding a briefcase full of secrets. Meanwhile, Budiman, now the editor-in-chief of a prestigious occult magazine, receives a cryptic package containing a suicide note from Heru, alongside unsettling photographs and drawings signaling cult activities emerging within the ominous structure of Mandara. Concerningly, the unsettling images indicate that Bahri was among the police officers who escorted Budiman to the observatory years ago.
In a tragic turn of events, a malfunctioning lift at Mandara leads to catastrophe, claiming numerous lives. As the storm rages and floods engulf the building, trapping its residents, Rini offers solace to Wisnu, a young boy mourning his mother, who fell victim to the calamity. Their shared grief uncovers a connection that transcends ordinary understanding. Wisnu discloses the secret sign language he learned from an occult book, which allowed him and his mother to communicate in silence, evading the cruelty of his abusive father.
As the flooding stirs something malevolent, supernatural disturbances begin to torment the residents. The power grid fails, prompting Bondi and his friends to discover haunting photographs in the building manager's apartment, illuminating the sinister truth of a cult congregation every 29 years on April 17th, a date now ominously drawing near. Meanwhile, Toni stumbles upon a hidden room revealing unsettling details of their deceased mother, Mawarni, who is intriguingly linked to a dark alter ego known as Raminom. This revelation triggers a cascade of memories for Rini, recalling her own mother's metamorphosis into an unfamiliar figure following her musical aspirations.
As threat levels rise and paranormal forces unleash their fury, Rini dares to open Bahri’s briefcase, unveiling severed fingers that insinuate his connection to the occult. In desperate search of answers, the siblings ascend to the top floor where Ian, their youngest brother, is revealed to have been taken by the cult. Wisnu's newfound sign language bridges the gap, allowing Ian to acknowledge his identity as a long-lost companion.
Just when it seems that despair reigns supreme, the eerie tranquillity of Mandara is shattered by the alarming return of the dead. Raminom orchestrates a relentless pursuit of destruction, targeting the siblings, Wisnu, and a few remaining survivors. An attempt to reach safety brings them face to face with Bahri, only to be ensnared by the cult’s fervent followers led by Ian. What unfolds is a grim spectacle as Ian, driven by dreadful joy, brutally executes Bahri in a horrific display of power. In the nick of time, Budiman intervenes, unleashing chaos through gunfire and providing the fleeting chance of escape. Wisnu uses his sign language for a desperate plea while Rini acts swiftly to incapacitate Ian. Amidst the chaos, they successfully break free via boat, where Budiman reveals the shocking history tethering Bahri to the cult — a web of manipulation and forced compliance with the Indonesian government, all initiated by Mawarni's ominous promise of fame.
The subsequent day, Darminah and husband Batara arrive at Mandara, visibly disheartened for having missed the night's grim rituals. Nonetheless, Batara reassures his wife that everything transpired perfectly, as evidenced by a photograph adorning the wall that depicts them alongside other dignitaries from the influential 1955 Bandung Conference, bearing testimony to their uncanny youthfulness.
