Season 1
The serial's plot begins with a man called Rathnavel (Riyaz Khan) falling in love with Parvathy (Khushbu), an enigmatic shape-shifting serpent, and the two of them being married. Nandini and Ganga, two twin daughters, were born to her. Ganga acquired human qualities, whereas Nandini inherited snake qualities. Parvathy offers her spouse Ganga after transforming him into a transgender person in order to spare him from her clan's murderous intentions. Subsequently, Rathnavel loses all memory and hands Ganga over to Manickam, the royal housemaid. Manickam is childless and believes Ganga is his daughter, raising Ganga in the palace. Then, Rathnavel adopts the name "Seyanayagi" and keeps up his devotion to the deity Karuppar.
6 years later
Prior to Rajashekar(Vijayakumar) and his party arriving to capture the "Kala Chakras" for financial gain, Parvathy and Nandhini were leading a tranquil life as followers of Kaatu Amman with Muniappa and his family. One day, after tricking Parvathy and Muniappa's family, Rajashekar and his pals Namboothiri, Vichu, Kumar, and Madhavi killed Parvathy and stole the three kaal chakras. Parvathy requests Nandhini that she should kill every murderer along with their whole family and return the lost Kaal Chakras. In the Rajashekar's palace, where Ganga is present, Namboodhiri locked Nandhini in a snake pit.
14 years later
The country girl Janaki (Malavika Wales) captures the heart of Arun Rajashekar(Rahul Ravi), son of Rajashekar, who marries her. Although Kavitha, Janaki's friend, also loved Arun, she died from heartbreak as a result of Janaki and Arun's marriage. Kavitha's sister Bhairavi(Gayatri Jayaram) swears to get revenge for her sister's demise. Soon after, Arun moved to Malaysia, where his palace was occupied by his wife Janaki. Months later, she has labour pains and gives birth to a child. However, Dharmaraj murdered her because he wanted his daughter to wed Arun. Turning into a ghost, Janaki defends her family.
6 years later
Ganga (Nithya Ram), who has grown into a beautiful young woman, has been doing pujas for the snake pit for the last 14 years without realising that her own sister is locked inside. Ganga consents to marry Arun because Rajashekar wants her to, and she promises to raise Arun and Janaki's daughter Devasena well.
She performed pooja to the snake pit the night before her marriage, and when her blood fell accidentally on Nandhini, she emerged twenty years later and entered the Ganga's body to exact revenge for the murder of her mother. After Ganga marries Arun, she begins her revenge. She intended to murder Arun and Devasena in order to demonstrate to Rajashekar what it feels like to die, but the Janaki spirit intervenes to rescue them. She thus brilliantly kills Kumar, one of the murderers, when he arrives at the palace and attempts to grab the kala chakra, but ends in vain. Nandhini departs Ganga's body to avoid being seen, and Ganga tells the authorities that she murdered Kumar and went to prison to prevent Nandhini from entering her body. However, Namboodhiri saw through it and Ganga was freed from custody. After learning of Nandhini's fate, Ganga confronts Rajashekar and begs him to provide the Kaal Chakras, but he refuses and tries to murder Ganga. Seyanayagi, however, goes to rescue Ganga. Ganga has been receiving therapy for months.
One Week Later
Nandhini (Nithya Ram) assumed a female form on one Full Moon Day, and she resembles Ganga. Rajashekar, in the meanwhile, commands Bhairavi, a magician in need of Kaal chakras, to change into Ganga and come to the palace.
Then, Nandhini captures Bhairavi, murders Namboodhiri and Vichu, and enters the palace dressed as Ganga in order to look for kaal chakras. After disturbed from her tapasya, Madhavi (Rekha Krishnappa) makes preparations to murder Nandhini. However, Rajashekar begs for forgiveness as Ganga comes back. They quickly discover that Nandhini resembles Ganga.
A few days later, Nandhini murders Rajashekar, which led Ganga to believe wrong things about Nandhini. After attempting to kill Nandini, Ganga realises they both are sisters and therefore clasp hands with Nandini. However, destiny intervenes, causing them to battle again until Madhavi seizes all three kaal chakras and gives rebirth to Namboodhiri. They both go to the Kaatamman temple and trap Nandhini. However, their scheme is foiled when Ganga bestows Nandhini with the three kaal chakras.
After killing Namboodhiri and Madhavi, Nandhini triumphs. Then, contrary to Parvathy's assertion that she should kill the Rajashekar's family, Nandhini transforms as stone serpent to punish herself. Ganga is left in tears when Nandhini and her are split apart once again. Ganga becomes pregnant after that, and the family has a happy life. However, when they are split up and the Nandhini-Ganga link is unbreakable, the last episode focuses on their sisterhood.
