The film is an adaptation of a play by Henrik Ibsen: An Enemy of the People.It is set in a small town in Bengal. Dr. Ashoke Gupta (Soumitra Chatterjee) is the head of a town hospital. Gupta's younger brother, Nisith (Dhritiman Chatterjee), is the head of the committees running the hospital and a temple. Both were built by a local Industrialist. The temple is also a big tourist attraction.

Dr. Gupta is convinced that the holy water of the temple is contaminated due to faulty pipe-laying. It is causing an epidemic in the town. He warns his brother Nisith.

Nisith, the Industrialist and other town officials reject the idea that holy water might be the cause of the epidemic. They refuse to close the temple to carry out the repairs.

Dr. Gupta wants to write an article in the newspaper to warn people, but giving-in to the pressure from the powerful people, the editor refuses to publish it.

Left with no alternative, Dr. Gupta organises a public meeting that is also sabotaged. And Dr. Gupta is proclaimed an enemy of the people.

Due to his medical condition after a heart-attack during making of Ghare-Baire, Satyajit Ray was told by the doctors not to do any location work. He was forced make a film totally in studio. For this, he thought a play would be more suitable rather than a story or a novel. Unfortunately, this constraint of shooting only in studio does mar the film as a whole. Ironically, when he began making films, Ray himself had said that he wanted to remove "the last trace of theatricality" from his work. In fact, Pather Panchali was so refreshingly fresh due to its location sequences.

Having said that, Ganashatru has its merits. As Ray commented in an interview with Andrew Robinson, his biographer:

"I found that for once one could play with human faces and human reactions, rather than landscapes, Nature in its moods, which I have done a lot in my films. Here I think it is the human face, the human character which is predominant."

This is true of not only Ganashatru but also Shakha Prashakha (Branches of the Tree) and Agantuk (The Stranger).

Soumitra Chatterjee, the young romantic Apu of Apur Sansar, now much matured and many more lines on his face, plays Dr. Gupta. As always, a superb performance. Ruma Guha and Mamata Shankar, as Dr. Gupta's supportive wife and daughter, also give commendable performances.