Sergeant is a psychological crime thriller about Nikhil Sharma (Randeep Hooda) who is an upright police officer and works in the London Metro Police and suffers from severe depression after losing a limb on duty. At home he can’t hit it off with his father (Arun Govil), whom he holds accountable for his mother's death. He also finds himself in a never-ending rivalry with Inspector Haider Ali (Adil Hussain), as he bags the position that Nikhil was about to get. Though Nikhil tries to come to terms with his situation but is hell bent upon to solve the mystery behind the unsolved critical case when he meets Monica and regains his confidence to get to the real culprits.