Dilli Gang is the story of an old man targeted by a dangerous gang, which preys on senior citizens living alone. The film is based on true incidents of increasing murders of aged men and women staying alone in metropolitan cities.

Vishambar Prasad and his wife Sujata have just married off their younger daughter amidst much pomp and gaiety. Soon after the wedding their only son Ashish flies back to Germany from where he had come only to attend his sister's wedding. The old couple is left alone in their big mansion in Delhi. A few days down the line it is revealed that Sujata is afflicted with multiple myeloma, a rare type of cancer.

Vishambar hides the news of his wife illness from their son and daughter. He thought it will distract his son and stunt his career in Germany. However, he is quick to send Sujata's reports to Germany for a second opinion from doctors there, saying it is the reports of his friend's wife. Surely, either he conceals Sujata's name on the reports with a whitener before sending it or he gets a fresh one from the doctor.

Meanwhile, in this city, there is a Gang of four whose livelihood is to murder and loot helpless and hopeless senior citizens of the city. They do this by pretending to be AC mechanics who offer free maintenance of ACs. Dilliwaalas open their doors to anybody who offers a free service. Then there are domestic servants and drivers who are hand-in-glove with the four criminals.

With so many incidents happening in the city, police started its hustle to catch people behind the cases. This gang finds new prey as Vishambhar Prasad after finding his circumstances related to life. Police team finds out about this and successfully save the family and catches criminals.