The writer and philosopher Denis Diderot completed the novel, La Religieuse, on which Guillaume Nicloux’s film is based, around 1780. However, the novel was not published until 1796, after Diderot's death. The work, which depicts convent life mostly in a rather harsh light, became a succès de scandale.

Yet La Religieuse was never placed on the Church’s index of banned books. Diderot’s intention was to write a critique, not so much of the Catholic church per se, but rather of the collaboration of Church, State and family in the imposition of enforced vocations. In mid-18th-century France, there were 5,000 convents and 55,000 nuns, while there were 3,000 monasteries and 30,000 monks. France differed significantly from other European countries in reversing the ratio. It is entirely possible that awful things could have happened within these convent walls, but Diderot's novel is not in the business of investigative journalism.

Controversy would resurface almost 200 years later when director Jacques Rivette adapted the infamous epistolary novel as a film in 1966. La Religieuse was banned in de Gaulle's France, before Jean-Luc Godard wrote an open letter and the ban on the film was removed in 1967.

As in the novel, the story is told through the sister's secret letters, which lends the authentic air of an actual historical document. However, it should be remembered that the original novel is in essence a melodrama which apparently began life as a series of letters, written by Diderot to con a writer friend. His gullible friend duly believed the letters to be from an actual religious sister who was suffering these awful torments.

The story shifts between decades, but its beginnings are in 1760s France when the teenage Suzanne Simonin (Pauline Etienne) is sent to a convent against her will. Her aristocratic family are unable to afford a dowry, due, it seems, to the demands of two elder sisters' costly marriages.

Once arrived at the convent, the kindly mother superior Madame de Moni (Francoise Lebrun)  tells her that no sister is obliged to take the veil unless she wishes to. Sadly, this is not the truth. The day of the profession of her vows arrives with all the attendant drama. The Archdeacon asks Suzanne if she is there of her own free will and she replies that she is unwilling to go through with her vows. The scene in which a vast white sheet, emblazoned with a red cross, is drawn across the supine sisters brings home the utter claustrophobia of her confinement. Suzanne is shown beneath the vast sheet, looking very distraught.

During a strained period spent at home, Suzanne learns something, which explains much about her predicament to date. The kindly Mother Superior agrees to take Suzanne back in, but different problems later arise with another Mother Superior, Saint Eutrope (Isabelle Huppert).

Muting the melodrama, as it were, Nicloux’s masterful film manages to present the - let's face it - sensational story with a restraining sense of naturalism. The Nun can be seen at the IFI.

Paddy Kehoe