A mysterious mastermind - Daredevil and his team forms a plan and commits bank heist to find the corporate looted people's money.
Thunivu is a mystery thriller movie that begins with a bank robbery, which leads to a sense of revenge against the government and the police. They threaten the government and police that if they let them go out without any trouble, they will not do any harm to the hostages over there. If they make any trouble, they will kill all the hostages. Some of the gang members stay outside to support them as they run away.—Baapofmovies.com
Radha, a dreaded gangster, and his men plan a heist at "Your Bank", one of the biggest privately-owned bank in Chennai, with the support of ACP Ramachandran. They plan to rob Rs. 500 crore on 21st May, coinciding with the Governor's party event at his residence. On the day of the heist, Radha and his men hijack the bank, only to discover that the bank is already hijacked by a mysterious man nicknamed Michael Jackson. The mysterious man is praised as a hero until he confesses his intention to hijack the bank himself, with outside support from his accomplice, Kanmani. The commandos arrive inside the bank, but get defeated. Jackson later makes a deal with Radha to help him rob Rs. 5000 crores, in exchange for a share of the money, for which Radha and his men reluctantly agree. He insisted a constable, Antony alias Anto to be the investigating officer.
When Radha finds that the bank locker contains only Rs. 1,510 crores, they decide to kill Jackson, only to be defeated. Dark Devil insists that Antony alias Anto, a police constable to be the negotiator, much to Ramachandran's ire. He uses a voice changer of Michael Jackson, tricking the people and the media into referring him as Michael Jackson. Ramachandran tries to kill Jackson with a sniper, only for him to make an explosion in a car parked nearby the bank, using a bomb. With the events being leaked to the media, city commissioner Dayalan is called in to handle the situation. While inspecting the bank, Dark Devil finds explosives, disguised as fire extinguishers, and deduces that a third team has also entered the bank, without him knowing.
The police tracks a van where Kanmani is guiding Jackson, but Kanmani destroys the van, and escapes. Ramachandran sends his men to trace Kanmani, but she kills them and exposes Ramachandran's involvement in the heist to Dayalan, who interrogates him, and he confesses that he along with his childhood friend Shyam, the Tamil Nadu Branch Head of Your Bank, planned the heist. Ramachandran tried hiring Jackson, who goes by "Dark Devil", for the job, but he refused. Ramachandran later hired Radha's gang for the job, without revealing that they will be killed after the heist. Radha and his gang join and assist Dark Devil after hearing Ramachandran's confession through bugs planted on Dayalan's base. Shyam flees from police after they learnt about his involvement, but is captured by Kanmani.
Meanwhile, Dayalan finds that Valavan was the one who wired and planted explosives in the drainage, and begins to search for him. He also learns that Dark Devil and his team actually died a few months ago. Ramachandran tries to prove that Dark Devil is alive by detonating a dummy bomb only to get killed when the bomb turns out to be a real one and explodes after the wire in it gets detached. Dark Devil learns from Kanmani that there are Rs. 25,000 crores available in the bank. Dark Devil tells Dayalan to arrange a meeting between him and chairman of Your Bank, Krish. As Dark Devil deduced, the third team, revealed to be some of the bank's staff, attack Radha and his team in the locker, before assaulting Dark Devil and hold him captive. Krish arrives and reveals that the third team were hired by him and tells them to destroy the bank's chest with explosives with hostage inside.
Krish also forces Dark Devil to reveal himself, where Dark Devil reveals that he and his teammates lived happily together like a family. After having committed a heist in Bangkok, Dark Devil's members, Jijo and Achara planned to get married. They all travelled to Araku Valley, Andhra Pradesh to arrange their marriage and celebrate, but they were ambushed by assailants sent by Krish and Shyam, who feared that they would reveal their heist plan to others. Jijo and Achara got killed, but Dark Devil and Kanmani managed to escape and the killers faked their deaths for the rest of their deal money. The duo reached the house of an old couple, who tends their wounds and revealed about his son Kavin, an honest bank official, who wanted to return the money to the people who invested in mutual funds. However, he was killed by Krish, and made it look like a mob did this during a strike.
Having learnt about this, Dark Devil and Kanmani decided to bring Krish and the bank officials to justice. After the revelation, Dark Devil defeats Krish and his team, where he forces him on live to reveal about his financial scam of the Rs. 25,000 crore, which was invested in the mutual funds, and the atrocities committed against people by the bank officials. Meanwhile, Shyam, who was made to wear a bomb vest is sent to Dayalan, where he reveals everything about the heist and Krish's involvement in it, before he is killed by Kanmani's phone call. Dark Devil also brings mutual funds chairman Harsha, who was abducted by Kanmani at gunpoint and Sunil Dutta, who was abducted from Mauritius by Dark Devil's men and was also responsible for stealing data from the NSE backup server of the Indian Stock Exchange. Sunil confesses that he invested in 10 companies belonging to Krish and reveals that the Rs. 25,000 crore is in the bank's secret chest locker.
With the help of a mole in the media, Krish falsely frames Dark Devil and his team as terrorists, and cuts the live telecast. Meanwhile, Dayalan learns from Rajesh that everyone in the bank are going to be killed, except Krish, before Commandos arrive and take control of the situation, and Dayalan is suspended. In the bank, Dark Devil opens the secret locker with the help of Radha and his men, only to find that the money is counterfeit money. Dark Devil locks Krish, Sunil and Harsha in the secret locker, before Krish reveals that the money is stacked in 25 of the 1500 containers of his ship, which he discreetly records as a video. The commandos open fire, with the bank severely damaged. Krish, Sunil and Harsha are killed in the secret locker by an explosive. Kanmani arrives in a fire truck stuffed with RDX, and threatens to detonate them, unless the hostages are released, forcing the commandos to cease fire. She along with Dark Devil, wearing masks, escape with the help of the public and reach a boat, planning to escape by sea, while Radha and his gang also escape in the ensuing chaos.
A chase ensues where Dark Devil, Kanmani, and the rest of their team shoot the commandos and coast guards, using an M2 Browning. However, they get shot and fall into the sea. Later, the media broadcasts the video which Dark Devil discreetly recorded, and Dayalan's suspension is revoked. Meanwhile, Dark Devil and Kanmani fake their deaths and escape using sea scooters and reached their boat, settling in international waters. Dayalan and his team board a helicopter to the ship, where they find the Rs. 25,000 crore.