In contrast to his more low-key output such as Piku and October, Shoojit Sircar’s new biopic takes on an epic subject: it retells the life of Udham Singh, an indelible figure in the Indian independence movement. While most famous for his headline-making assassination of Michael O’Dwyer, a former governor of Punjab who oversaw the horrific 1919 Amritsar massacre, Singh remains something of a historical question mark and many of his biographical details are wrapped in mystery.

Reflecting such ambiguities, the film jumps across continents and timelines as it attempts to illustrate Singh’s arduous journey from his upbringing in an orphanage in Punjab to his final days as a political martyr in London. Scotland Yard’s investigation of the assassination takes up most of the running time, during which Singh’s origin and motivations are slowly revealed, Citizen Kane-style. This approach, unfortunately, proves the film’s weak spot, obscuring the charisma of the dashing Vicky Kaushal in the title role, and telling the story from imperialist viewpoint of the probing detectives. Singh himself remains a remote figure, filtered through endless sessions of questioning and torturing.

The film finally coheres towards the end during a lengthy sequence depicting Singh’s political awakening in the massacre’s aftermath. Released from the straitjacket of the investigation scenes, Kaushal delivers some of the film’s most memorable moments as a young man shellshocked by the horrors of colonialism. Still, Sircar’s treatment of the event is questionable, with voyeuristic shots of victims’ gaping wounds. Treading such terrain requires a deft directorial hand, and Sircar’s usual assuredness is missing from this meandering blockbuster.

• Sardar Udham is on Amazon Prime Video from 16 October.