Indian army officer Lieutenant General Nikhil Bakshi addresses a group of Indian soldiers aboard the INS Viraat, detailing a woman's exploits while serving as an undercover agent of the Research and Analysis Wing (RAW), India's external intelligence agency, in Pakistan.The story flashes to events preceding the Indo-Pakistani War of 1971. Hidayat Khan is the son of an Indian freedom fighter and agent posing as an informant for the Pakistani government. He wishes to make his 20-year old daughter Sehmat an agent and continue the family tradition of being in service to the country as a last wish before his impending death from lung cancer. Sehmat leaves college against the wishes of her mother Teji Khan, and to prepare her to spy, she is hastily trained by senior RAW officer Khalid Mir and his assistant, a young Bakshi, in various fields, including martial arts and shooting. She learns of other agents in Pakistan and their contacts, and practices converting text information to Morse code, which she has to use while transmitting information to India.Khan uses his friendship with Brigadier Syed of the Pakistan Army to get Sehmat married to his son, Iqbal Syed, another military officer. After the marriage and migration to Pakistan, Sehmat quickly settles into her married life, adjusts to a new country, and establishes the trust and confidence of her in-laws. Brigadier Syed is promoted to Major General shortly afterwards, which results in crucial national security documents and senior members of the country's defense forces passing through his house. Sehmat soon establishes communication channels with her handlers back in India and starts relaying information. Meanwhile, she falls in love with Iqbal and develops physical proximity with him.Eventually, Sehmat spots information related to the planning of an offensive against India and, at great risk, is able to gather the necessary details and pass them on. One of the servants, Abdul, discovers the truth about Sehmat and rushes out to inform the others. She chases him and is forced to murder him with a jeep to avoid exposing her cover. The event takes a heavy emotional toll on her. The information she passed on points to the planned attack on the Indian aircraft carrier INS Vikrant, then deployed in the Bay of Bengal and provided one of the initial warnings to the threat.Sehmat is left with no choice but to also kill Mehboob Syed, Iqbal's brother and an army officer after he begins investigating Abdul's death and finds her suspicious. Sehmat is mentally disturbed, having widowed Munira, Mehboob's wife, but quickly recovers. She is eventually discovered as a spy by Iqbal, who is heartbroken by the revelation. Iqbal confronts Sehmat with the police but dies from a bomb thrown by Khalid Mir to cause her death should she be caught. Sehmat is alive, having switched places with another burqa-clad agent. She realizes the insignificance of relationships and humanity in this line of work. Broken by the destruction of a family by her hand and everything she has seen and had to do, Sehmat requests Khalid to allow her to return to India. After she does, it is discovered that she is pregnant with Iqbal's child. She says that she will keep him and raise him alone.With Sehmat's findings, the INS Rajput sinks the Pakistani submarine PNS Ghazi off Visakhapatnam's coast. This starts the Indo-Pakistani War of 1971, which ends with the Pakistani Instrument of Surrender, an Indian victory. Bakshi concludes his speech, with Samar Saeed, Sehmat's son, among the addressed officers.