Living in a middle class orthodox family of Old Hyderabad, Bilqis Ahmed aka Bobby (Vidya Balan) is a wannabe private detective. To pursue her passion of spying Bobby solves petty neighbourhood cases, such as helping Tasawur (Ali Fazal) a TV show host, to get rid of marriage proposals brought home by his parents. Bobby finally gets her big break when a rich NRI Anees Khan (Kiran Kumar) hands her a case of finding two missing girl named 'Nilofer' and 'Amna' with a birth mark on their hand and shoulder respectively. To solve the case Bobby takes up many getups such as 'beggar', 'peon', 'hawker', 'nerd student', 'astrologer' and even a fake ' TV producer'. After locating the targets, Khan pays her a tremendous fees and also offers huge amount to both girl's fathers for reason unknown to Bobby. Khan also hands over his 3rd and final case of finding a boy with a missing toe named 'Ali'.
Meanwhile Bobby and Tasawur's family fix their marriage leaving both into dilemma of how to get rid of this situation. A local goon Lala (Arjan Bajwa) also offers a case to Bobby to break Lala's girlfriend's marriage, which is fixed by her mother forcefully. On Bobby's denial Lala makes her realise that she has been helping the NRI for a wrong cause. Doubting on that Bobby tries to know the wereabouts of the two girls, but gets to know that both girls are missing. Scared and shocked Bobby takes help from Tasawur and sneaks into Khan's hotel room to check his background only to be caught and thrown out. But Bobby manages to get hold on Khan's diary and his old photograph, which later gets in hands of Lala who since then starts following Bobby.
Khan now suddenly goes into hiding and Bobby starts searching for him with the belief that Khan will not leave the town without his third target Ali. With the help of clues in Khan's diary such as a London based library's stamp and a Biryani order from a local restaurant, Bobby gets to know about Khan's background. Later, Khan is shown following a man called Ali which later turns out to be Bobby's trap to capture Khan. With the twist in the climax, it is revealed that the the three person Khan was looking for were his long lost children during communal riots. Khan has offered money to both girls foster parents for their good future and the missing girl has actually been sent to London for higher studies. Tasawur also enters the scene along with Lala who is Khan's long lost son 'Ali'. Film ends with Bobby becoming a famous detective, while she and Tasawur now in love with each other but are still confused about their marriage.