Thiruvin Kural

A sack of concrete falls from a building, severely injuring Marimuthu and sending him to a government hospital. Thiru, his sister Chithra, and Bhavani rush to the hospital to be by his side. At the hospital, they meet liftman Aarumugam who tells Thiru to use the stairs, and Thiru grows angry when he sees Aarumugam watching Bhavani and Chithra.

The next day, Thiru goes to fetch coffee for his father at a tea stall, where Aarumugam confronts him and pushes his head back in anger. Thiru fights back and knocks him down. This marks the start of Thiru's ongoing conflict with Aarumugam.

Thiru learns that Aarumugam and his colleagues Suresh, Vinoth, and Santhan are criminals who rob the rich and even kill people. This revelation deepens the danger Thiru faces as he tries to protect his family. The group’s criminal intent becomes more personal to Thiru.

Aarumugam and his cronies attempt to steal money from a wealthy man, but Thiru intervenes and foils the plan. Their plan spoiled leads them to plot revenge against Thiru. The tension between Thiru and the criminals escalates quickly.

To exact revenge, Aarumugam and the others blackmail Dr. Venugopal into injecting a drug into Marimuthu, causing his condition to deteriorate. The hospital scene becomes more perilous as Marimuthu's health worsens. Thiru grows more desperate to protect his father.

The criminals escalate their manipulation by using nurse Mullai to obtain a doctor's signature by deception. Thiru wheels his father to the next block, but staff misread his card as a food token, delaying care and causing Marimuthu to vomit blood. The situation pushes Thiru toward a breaking point.

Aarumugam threatens Thiru by calling to kill his niece Sharmi. Thiru rushes to save her, but Sharmi is pushed into a water tank and admitted to the hospital. The threat intensifies the threat to Thiru’s family.

News channels cover the hospital turmoil and police begin investigating the four criminals. The growing public and official attention adds pressure on the criminals and heightens the stakes for Thiru. The investigation frames the broader crisis around the hospital.

The four criminals hide at their regular place and burn the dead bodies to destroy evidence. During internal discussions, Aarumugam learns that Vinoth betrayed them by telling Thiru what happened. The criminal alliance starts to crumble under pressure.

Thiru locates the criminals' hideout, confronts them, and kills Aarumugam and his three colleagues. He also rescues Venugopal's wife, who had been abducted. The climactic act marks Thiru’s triumph over the criminals.

Back at the hospital, Thiru's grandmother reveals that Marimuthu is missing. Thiru searches the streets and finally finds him on a roadside bench. The emotional reunion underscores the danger they faced and the tenuous hope for his recovery.

Marimuthu admits he cannot bear the pain and fears dying before Thiru's wedding. Thiru and Bhavani are married, and Marimuthu and Sharmi are healthy, bringing a hopeful ending to the ordeal. The family moves forward with renewed happiness and relief.