Ek Din Achanak (Hindi: एक दिन अचानक; English: Suddenly, One Day) is a 1989 art film directed by Mrinal Sen, based on the 1977 Bengali-language novel Beej by Ramapada Chowdhury.

[1] One evening, in the midst of torrential rains, a professor (Shreeram Lagoo) goes out for a walk and fails to return.

The professor's son Amit "Amu"(Arjun Chakraborty) establishes his fledgling business; his younger daughter Seema (Roopa Ganguly) resumes her studies at college; and his elder daughter, Neeta (Shabana Azmi), the backbone of the family, returns to her office job.

Neeta has a very patient and supportive boyfriend Alok (Anjan Dutt), but the relationship is stuck in a holding pattern.

Their hesitant attempts to piece together the professor's state of mind before his disappearance raise more questions than they answer: Was he having an affair with a former student (Aparna Sen)?