Season 1 (In chronological order)
In the early 90s, a wealthy man named Rathnavel Boopathy falls in love with an enigmatic shape-shifting serpent named Parvathy, and the two get married. They move to a distant village to escape from Parvathy's evil clan, who are against her marriage. Parvathy gives birth to twin daughters—Nandini and Ganga. Ganga acquires human qualities, whereas Nandini inherits snake traits.
To protect Rathnavel from her clan’s murderous intentions, Parvathy transforms him into a transgender person and lets him escape with one of the daughters, Ganga. She escapes with the other daughter, Nandini. Subsequently, Rathnavel loses all memory and hands Ganga over to a royal housemaid named Manickam. Manickam, who is childless, raises Ganga as his own daughter in the palace where he works. Rathnavel takes on a female name "Seiyanayagi", and continues his devotion to the deity Karuppar.
Parvathy seeks shelter in an abandoned temple of Kaatu Amman in the forest, where she regains her powers as "Shiva Naagam" through the influence of the three Kala Chakras—a set of sacred spiritual objects present in the temple. From then on, Parvathy takes up the responsibility of protecting the Kala Chakras. Meanwhile, Nandini is destined to remain in serpent form until she turns 26, at which point she will attain a human form and the status of "Shakthi Naagam."
- 6 years later
Parvathy and Nandini live peacefully as devotees of Kaatu Amman, along with the temple priest Muniappa and his family. A rich businessman named Rajashekar and his five friends(a magician named Namboothiri, three business partners- Kumar, Vichu, Rajesh, and Namboothiri’s sister Madhavi) arrive to steal the three Kala Chakras protected by Parvathy—for personal gain.
One day, Rajashekar and his friends deceive Parvathy and Muniappa’s family, murder Parvathy and steal the three Kala Chakras. Nandhini comes to rescue Gayathri (Muniyappa's daughter) from one of the murderers Rajesh, and kills him. Gayathri asks Nandhini to go to the temple. Gayathri was then taken by the village people. When Nandini reaches the temple, she witnesses a dying Parvathy who asks Nandini to avenge her by killing every murderer along with their families and reclaiming the stolen Kala Chakras and then she dies. Nandhini goes fiercely to avenge all the 5 but with the 3 kaal chakras power, she faints down and gets captured by the murderers.
The Kala Chakras only have power as long as Nandini is alive. So, they decide to trap Nandini at Rajashekar’s palace, where her twin sister Ganga lives. Namboothiri traps Nandini in a snake pit with magical protection, rendering her immobile. She is sealed in the snake pit with a magical law stating that "Nandini can never break free until the blood of her true devotee falls on her skin".
- 14 years later
Arun Rajashekar, the son of Rajashekar, falls in love with a village girl named Janaki and marries her. Kavitha, Janaki’s friend who also loved Arun, commits suicide after the marriage. Her sister Bhairavi, a powerful magician, vows revenge. She kills Janaki’s father and sets out to destroy Arun’s family.
Soon after, Arun moves to Malaysia, leaving his pregnant wife Janaki behind at the palace. During this time, Janaki bonds well with the grown-up Ganga, who works as a maid in the palace. Months later, she gives birth to a child, but the baby is secretly swapped with a dead child, making everyone believe that Janaki's child died. Dharmaraj—Arun's uncle—kills Janaki with the help of his son Moorthy and their friend Balaji, hoping his own daughter Maya can marry Arun. Arun is devastated after Janaki's death and goes into depression. Janaki returns as a spirit to bring back her child and protect her family.
- 6 years later
Ganga, now a young woman, has unknowingly performed daily poojas at the snake pit for the past 20 years and becomes a devotee of the snake inside, unaware the snake is her own sister who is trapped within. Janaki’s spirit tries to give magical clues to Arun and succeeds in bringing back her real daughter, Devasena to the palace, who had been swapped at birth. Arun agrees to remarry for the sake of his daughter Devasena. Meanwhile, Rajashekar’s wicked sisters Devi and Manju, along with Janaki’s murderer Dharmaraj, compete to get their daughters married to Arun. However, Janaki’s spirit thwarts all their plans and kills Balaji, one of her murderers. Eventually, Ganga agrees to marry Arun at Rajashekar’s request and promises to raise Devasena with love. Meanwhile, Janaki continues protecting Arun from Bhairavi’s attacks.
The night before her wedding, Ganga’s blood accidentally spills into the snake pit during pooja, breaking the 20-year magical protection around Nandini. Nandini enters Ganga’s body to avenge her mother’s death. After Ganga marries Arun, she begins her quest for revenge. Nandini plans to kill Arun and Devasena to make Rajashekar suffer but is stopped by Janaki’s spirit. Nandini successfully kills Kumar, one of the murderers of Parvathy, but fails to attain the Kala Chakras. The battle between Janaki’s spirit and Nandini escalates—one fighting to protect the family, the other seeking its destruction. Nandini leaves Ganga’s body to avoid detection. Ganga, taking responsibility for Kumar’s death, surrenders and is imprisoned to prevent Nandini’s return. Namboothiri, however, sees through this and ensures Ganga is released. Ganga starts despising Nandini without knowing the true story behind Nandini's revenge.
Meanwhile, Bhairavi seeks the Kala Chakras after knowing about its true powers. An evil witch named Saamundi, also seeks the Kala Chakras for gaining power. Multiple battles occur amongst various people for getting the ownership of the Kala Chakras. Janaki's lookalike named Seetha arrives into Ganga's life, unknowingly creating conflicts between her and Arun. Ganga leaves the house due to misunderstandings and ends up learning about Nandini’s true story. Ganga confronts Rajashekar and begs for the Kala Chakras. But he tricks her and tries to kill her, but Seiyanayagi rescues her and treats her in secret.
- 1 week later
On the night of a full moon, on her 26th birthday, Nandini attains a female form identical to Ganga. But no one knows the true form of Nandini's appearance. Meanwhile, Rajashekar is scared that his son will discover Ganga's murder and commands Bhairavi to disguise herself as Ganga and return to the palace to obtain the Kala Chakras. Nandini makes use of this chance and captures Bhairavi, kills Namboothiri and enters the palace posing as Ganga to search for the Kala Chakras. Madhavi, the final murderer of Parvathy, emerges from her long penance to try and kill Nandini. Rajashekar, sensing danger, pleads for forgiveness when Ganga returns. It soon becomes clear that Nandini and Ganga look identical.
A few days later, Nandini kills two other murderers- Vichu and Rajashekar, which causes Ganga to misunderstand her. Bhairavi, now reformed, forgives Arun and assists Nandini in her quest for the Kala Chakras. Meanwhile, Janaki kills Dharmaraj and Saamundi to protect her family. Madhavi seeks the assist of Janaki's spirit to help her kill Nandini. Janaki agrees to protect her family from Nandini. Ganga initially tries to kill Nandini but eventually learns from Seiyanayagi that they are sisters. The two join forces, but fate separates them once again when Madhavi gains possession of all three Kala Chakras and resurrects Namboothiri.
The entire family now realize the evil intentions of Madhavi and Namboothiri. Together, Madhavi and Namboothiri trap Nandini in the Kaatu Amman temple. Their plan is thwarted when Ganga gives Nandini the three Kala Chakras. With Janaki’s spirit helping her, Nandini kills both Namboothiri and Madhavi. Contrary to Parvathy’s dying wish that the entire Rajashekar family be destroyed, Nandini chooses to spare the remaining members and turns herself into a stone serpent as penance. Ganga is heartbroken by their separation, but Nandini promises to visit her once every year. Ganga later becomes pregnant, and the family begins a new, peaceful life. Though separated, the bond between Nandini and Ganga remains unbreakable. The final episode focuses on their enduring sisterhood.
