Inspector Vijay Prakash is a publicity-hungry officer, who loves to be in the media limelight as he wants to undo hurdles in his profession due to the reputation of his absconding father Chandra Bose- a former spy who gets framed as a national traitor. Vijay is raised by his uncle Paavadaisaami, who is also a cop by profession, as his entire extended family commits suicide out of shame when the news of his father's treason goes public. Vijay tries to woo his friend Shalini, a lawyer, for all time, but she refuses to accept him due to his fame-seeking attitude.

Meanwhile, Vijay is assigned the mission of catching a mastermind, who has stolen a highly classified file in Rajaji Bhavan, which containing background information of agents that have been working in the RAW since the 1980s. Viewing this as a golden opportunity to build his reputation, Vijay starts investigating the case and learns that a social activist named Sameera Thomas has stolen the file. Vijay tries to find Sameera with the help of her son, Timothy "Timmy" but finds that Sameera's corpse has been found and she was declared a national traitor. Taking the case personally, Vijay investigates and learns that Sameera was interrogated about a person named Sardar, but she did not reveal anything.

Through Sameera's laptop, Vijay finds that Sameera has been protesting against a water packaging company, run by a former NSA officer Maharaj Rathore, whose project One India One Pipeline is expected to unify and control the supply of potable water across India. As per the research information obtained from Sameera's laptop, the company has been producing toxic water, as a by-product, which contains carcinogens and other harmful chemicals. As a result of the drinking water, Timmy was diagnosed with sarcoidosis. Heartbroken, Vijay and Shalini learn that Sameera was heading to a train station to meet an accomplice. He finds her accomplice at the train station and manages to capture him, but the accomplice gets killed.

Amongst his belongings, Vijay checks a book that contains a destination address (which Vijay had previously seen with Timmy as he posted a letter to their relative Victor on the advice of Sameera) at the Chittagong prison in Bangladesh. Meanwhile, the RAW agency receives information about Sameera's letter, which is named CODE RED. Rathore contacts the NIA and tries to get the warden to finish off Sardar, but he manages to escape from the prison. Vijay finds a location from the accomplice's belongings, which is a petrol bunk with a secret tunnel. Vijay finds a file after a brawl with an assassin, who also came to retrieve the file. Going through the file, Vijay learns that Sardar is actually Chandra Bose.

Past: In 1985, Sardar is working incognito, as a spy for RAW, by disguising himself as a drama artist and lives happily with his family. Sardar falls in love with Indhra Rani (who also loved him, but later learns about his profession) and they get married, and their son Vijay is born. One day, Sardar receives his next assignment to investigate the India-Pakistan border, where the agency learns about suspicious activities lurking at the border. Being a master-of-disguise, Sardar manages to escape with a photo and a type-written translated copy of a file, written in Chinese.

After detailing the file to his superior officers Rathore and Victor, they learn about China's plan to spread false news about poisoning the country's water through Pakistan and implementing pipelines to monopolize India's water supply through One India One Pipeline. They also learn that a mole, codenamed Laughing Buddha, in their agency, is helping China with the mission. Rathore and Victor sends Sardar to track down Laughing Buddha. Sardar gets in contact with another agent codenamed Cockroach, and deduces that the NSA Chief, P. K. Abraham, is actually Laughing Buddha. They manages to capture him in Bangladesh. However, Rathore gets consumed by greed and decides to eliminate Abraham.

Sardar tells Rathore that he will eliminate Abraham, to which he agrees, and Sardar gets imprisoned for 32 years in Bangladesh prison under the account of falsely holding multiple passports, while Rathore falsely frames Sardar as a national traitor and resigns himself from RAW. Afterwards, Rathore secretly joins China and became the head of One India One Pipeline. After learning about Rathore's treachery, Sardar gets enraged, but remembers that he has stored the copies of the file and hidden them in a safe locker. Through Sameera, Sardar decides to finish the mission.

Present: Rathore heads to the RAW's vault and tries to track the person who posted the letter to Sardar, while Vijay learns that Paavaidaisaami is one of Rathore's men, where he is brought to the RAW vault. Under the orders of Chief Chandra Mohan, the RAW agents try to secure Victor and bring him into the headquarters, while Rathore sends his men to kill Victor, but Sardar arrives and kills all of them. Accompanied by Timmy to the headquarters and in the guise of Victor, Sardar and Timmy arrive at the headquarters and defeat the other agents. Inside the vault, RAW agents try to hold back Sardar unsuccessfully.

Rathore confronts Sardar and reveals that he had killed the latter's family after he came to know that Rani had eavesdropped on their conversation using the secret frequency of Sardar and Rathore, after killing them all he staged it like a suicide, but left Vijay alive deliberately to make people believe that his family committed suicide out of disgrace and to make him bear his father's disgrace. Vijay also learns about this and gets enraged. Sardar, along with Timmy escapes in a truck filled with sodium. Rathore learns this and deduces that Sardar is planning to destroy the pipeline, and heads to the water plant, to stop him.

Sardar manages to reach and defeat the guards at the water plant. He destroys the pipeline and stops the hazardous water from flowing through villages. Upon finally killing Rathore, Sardar meets Vijay and tells him that he cannot live a peaceful life as he is committed to being a spy for the country and leaves. Sameera is proven innocent, while Sardar heads towards another mission and the Central Government cancels the One India One Pipeline. However, Vijay is suspended from the police force, for his inability in nabbing Sameera and Sardar alive.

In a post-credits scene, Chandra Mohan reveals to Vijay that he was the one who pulled the strings, in his suspension from the police force, and appoints Vijay to work as a spy, for RAW. Vijay is given a mission in Cambodia, with a codename.