In war torn Calcutta during the 1940's, Byomkesh Bakshy, fresh out of college, pits himself against an evil genius who is out to destroy the world.

Vidya Bagchi (Vidya Balan) arrives in Kolkata from London to find her missing husband Arnab Bagchi. Seven months pregnant and alone in a festive city, she begins a relentless search for her husband. With nothing to rely on except fragments from her memories about him, all clues seem to reach a dead end when everyone tries to convince Vidya that her husband does not exist. She slowly realises that nothing is what it seems. In a city soaked in lies, Vidya is determined to unravel the truth about her husband - for herself and her unborn child - even at the cost of her own life.