An orphan, Simhadri (Jr. NTR) is 'adopted' and grows up under the care of Ram Bhupal Varma (Nassar) and family in Visakhapatnam. The bond they share is like a father and son. Kasturi (Ankita) is the granddaughter (youngest daughter's daughter) of Ram Bhupal Varma. Kasturi likes Simhadri a lot. Once a week, Simhadri visits a mentally challenged girl called Indu (Bhoomika Chawla). He entertains her and provides money to her caretakers (Rallapally and Ragini).
When Ram Bhupal Varma and his wife discover Kasturi's wish to marry Simhadri, Ram Bhupal Varma decides to get them married. He makes a formal announcement to officially adopt Simhadri. At this time, it is revealed that Simhadri is very close to Indu. The alliance breaks off when Simhadri refuses to leave Indu (who is suspected to be his mistress).
Meanwhile, two separate groups are in search of Simhadri. They find him at the banks of Godavari River along with Indu. In the ensuing confrontation between one group (gangsters) and Simhadri, Indu gets injured. Simhadri is helped by the second group who call him 'Singamalai Anna' (Brother Singamalai).
When Indu comes back to her senses, she remembers her past and the first thing she does is stab Simhadri with an iron pole. Simhadri is hospitalized in critical condition. Then we see many buses carrying hoards of people demanding to see 'Singamalai Anna'. The leader of the second group who was searching for Simhadri explains 'Singamalai Anna' story in a flashback.
In the flashback, it is revealed that Ram Bhupal Varma's oldest daughter Saraswati (Seeta) elopes with her lover, a Keralite named Aravind (Bhanu Chandar). After some harsh words and saddened over Ram Bhupal Varma's rejection over her choice to marry her love, they both settle in Kerala.
Learning of the sadness surrounding Ram Bhupal Varma and his wife, Simhadri takes up the job of uniting the family and visits Thiruvananthapuram (Trivandrum). He joins the medical and spiritual therapy spa operated by Saraswati and her family under the disguise of a patient.
He finds that Indu is the first granddaughter of Ram Bhupal Varma. He convinces the separated family to reunite and ask for forgiveness. During this time, Saraswati is killed by a local goon Bala Nair (Rahul Dev). A don named Bhai Saab (Mukesh Rishi) controls the mafia of Kerala. Nair and Bhai Saab belong to the same mafia.
Simhadri takes the law into his hands and eradicates Bala Nair and his small gang in Kerala. The local Kerala people starts calling him 'Singamalai'. In the ensuing scenes, Simhadri finds himself developing into 'Singamalai', eradicating Bhai Saab's network and illegal activities. Indu finds herself alone and constantly worrying about him. She proposes to her father that they should return to Andhra Pradesh because she cannot stand their home without her mother and Simhadri ignores her now.
Indu and Aravind decide to return to Visakhapatnam. Simhadri receives a call that Indu's father is carrying a bomb in his briefcase. Aravind is seen rushing to catch a moving train and Indu was about to lend him a hand. Unable to warn him, Simhadri has two choices: to let Indu's father die, so people on the train can live or let the bomb kill everyone on board, including the father and Indu herself.
Simhadri chooses to the first option. As soon as Aravind catches the train bar handle, Simhadri shoots him in the back. Surprised at Simhadri's action; Indu jumps off the train to catch her falling father and she gets hit her head against a pole, causing her amnesia and becomes mentally challenged in the process.
After the flashback ends, people are seen and heard chanting Singamalai Singamalai outside the hospital. Bhai Saab and his men arrive at the hospital to finish off Simhadri. But Simhadri has gained consciousness with the help of his friends, police and family (now reunited), he takes down Bhai Saab and his army.