The film's title comes from the historical date of 16 December 1971, the day of victory of Bangladesh, and also the day on which Pakistan had signed the document of Liberation of Bangladesh.
Indian Revenue Service officers are on a mission to arrest Pakistani terrorists, who have a plan to plot to a nuclear bomb in Indian capital, New Delhi. IRS have to decode their plans and moves to stop the destruction of the city.
Major General Vir Vijay Singh, Vikram, Sheeba, and Victor are the IRS officers from Revenue Intelligence department. The general is blamed for murder of a corrupt senior and is suspended. Vikram and Sheeba share some romance between them. Hi-tech equipment, like mini spy cameras, computers, and communication devices are into use for the purpose. They discover illegal Swiss account transactions.
Sonal Joshi, an Indian working in New Zealand help them identify the account, Kaala Khanjar which belongs to terrorist organization, to which money is being transferred. This organization and Dost Khan smuggle a Russian nuclear bomb to India, which has to be exploded on the 16 December.
Some hard-lined Pakistani soldiers were angry at the surrender of 1971 Pakistani dictator, and wanted to fight the incomplete war as per their accord. They came together as communal soldiers to plan terrorist attacks on India.
Dost Khan, Pakistani army man, who had to forcefully surrender in 1971 war. The team manages to know about the plan through Meer Jafar, and a child helps them find the location. Remote Radiation Sensors in satellites and innumerable beggars in the city identify the actual location of the bomb.
Dost Khan comes to know that the team has killed most of his men and sets the nuclear bomb in a few minutes ready for explosion. Problems arise as the bomb can be defused by exclusive voice command, only from Dost Khan: Dulhan Ki Vidaai Ka Waqt Badalna Hai. They manage to make him speak the code into a novelist way and he says the code in fragments which are combined and bomb is diffused.