Following the epic Kurukshetra War, Ashwatthama (Amitabh Bachchan) embarks on a dark mission to eliminate the unborn child of Uttara (Malvika Nair). For this heinous act, he is cursed by Krishna (Krishnakumar), the eighth avatar of Vishnu, destined to wander the earth as an immortal being, forever a witness to the suffering of humanity as society crumbles during the Kali Yuga. His divine gem, a source of immense power, is ripped from his forehead, and it is foretold that his chance for redemption lies in protecting the mother of Kalki, Vishnu's tenth and final avatar, during the bleak days marked by a poisoned atmosphere and a lifeless river Ganga.
Fast forward to 2898 AD, six millennia after the harrowing events of the Kurukshetra, Kasi emerges as the sole bastion of civilization amidst a desolate, post-apocalyptic landscape presided over by Supreme Yaskin (Kamal Haasan), an omnipotent, two-century-old tyrant. The river Ganga lays dry, while an unusual bright star—last seen centuries ago—casts its glow in the sky.
Yaskin's rule is enforced from the 'Complex', a grand inverted-pyramid structure hovering over the city. Here, his command is held firm by Commander Manas (Saswata Chatterjee), Counsellor Bani (Anil George), and a relentless army, all geared up to subdue any insurrection, particularly from the elusive rebels of Shambhala, who await the prophesied arrival of Kalki.
In this grim universe, fertile female refugees are captured and taken into the Complex for Project K, a covert operation designed to create a powerful serum for Yaskin through the use of artificially inseminated fetuses. Yet, the serum only becomes effective after 150 days of gestation, with the grim reality being that none of the fetuses or the pregnant women survive the extraction procedures. Project K's scientists lament that the wombs are too frail to bear the potent concoction.
A young girl, Raia (Keya Nair), cleverly disguises herself as a boy to escape the dreadful conscription into this project, thanks to the assistance of Veeran (Pasupathy), a brave soul from Shambhala devoted to protecting Divya (Mrunal Thakur). However, Veeran soon realizes Divya is not the foretold mother of Kalki as evidenced by a lamp that does not ignite in her presence.
Tragedy strikes as Divya is killed by Manas while attempting to extract information about Shambhala, and Veeran meets his own end while warning Manas about Kalki's impending arrival.
Meanwhile, Bhairava (Prabhas), a hardened bounty hunter seeking riches to gain entry into the Complex, harbors a past marred by betrayal—having been orphaned during the war and sold out by his guardian Pilot (Dulquer Salmaan) for a chance at survival within the Complex. Roxie (Disha Patani), his love and financial backer, works within the Complex, and their paths intertwine as they navigate the glamour and danger contained within its walls.
As fate intertwines their lives, Raia discovers refuge within a cave, where she unexpectedly encounters Ashwatthama. In a twist of fate, she unknowingly returns his divine gem back to him, leading both to the realization that they must locate the woman carrying Kalki. In a barren desert, Counselor Bani uncovers Arjuna's Gandiva, yet no force can wield it without its ancient consent.
In the Complex, SUM-80 (Deepika Padukone), a project subject concealing her disturbing 150-day pregnancy, is forced against her will into the extractive procedure. Despite failing all seeding tests, SUM-80 finds herself pregnant, which leads to a terrifying encounter with Manas during her extraction. A daring rescue by a fellow Shambhalan rebel named Lilly saves her from a grim fate, however.
As they flee towards Shambhala, their journey is met with peril as bounty hunters launch an ambush. In a selfless act, Kyra (Anna Ben) sacrifices herself to ensure Sumathi's escape. Meanwhile, Bhairava discovers this high-profile escape and pursues them, believing this bounty will assure his entry into the Complex.
Chaos erupts as soldiers confront the rebels, and Ashwatthama and Bhairava clash in a battle for Sumathi—but ultimately, Ashwatthama prevails and leads her to safety in Shambhala, where the sacred tree of life flourishes in the presence of the awaited mother of Kalki.
It soon dawns on Bani that Ashwatthama is fiercely guarding the mother carrying the divine child and that the mysterious Gandiv has resurfaced with her arrival. The planets are soon poised for alignment, signaling a cataclysmic eclipse—a historical event that hasn't occurred in 6000 years.
Within this fierce struggle, Ashwatthama reveals that his seemingly unremarkable walking stick holds an ancient power—Vijaya Dhanush, forged for Karna (Prabhas) during his life in the Kurukshetra War, a weapon fabled to be wielded only by its rightful owner.
As tensions escalate, Bhairava cunningly strikes a deal with Manas—capturing Sumathi would earn him passage inside the Complex. Deceit flows thick as he persuades a captured rebel, Luke (Harshith Reddy), to lead him to Shambhala under false pretenses.
Once within, chaos ensues: Mariam ([Shobana]), the leader of Shambhala, makes a desperate attempt to guard Sumathi, but tragically falls to Manas's blade. As the conflict rages, both Ashwatthama and Bhairava swirl into the fray to save the divine mother. Yet, in a moment of distrust, Ashwatthama incapacitates the enthralled Bhairava before Manas's forces capture him within their grasp.
In a twist of fate, a latent power resurfaces when the fallen leaf from the tree of life fortuitously lands in Bhairava's hand, awakening the essence of Karna within him. Empowered with this newfound strength, he vanquishes the soldiers, even killing Manas in fierce combat. As the dust settles, Bhairava becomes the beacon of hope for Sumathi, determined to escort her to safety, while Ashwatthama perches helplessly as a prisoner.
In a climactic revelation, Yaskin consumes the serum drop extracted from Sumathi's fetus, transforming into a youthful, formidable being. With newfound strength, he wields Arjuna's bow, Gandiva, vowing to capture Sumathi and reshape the world in his twisted vision.
