With the BFI's season of Spanish cinema after Franco in full swing, it was only a matter of time before Pedro Almodóvar turned his hand to religion. 

Released in 1984, Dark Habits is Almodóvar's third film and - if the puntastic title wasn't a big enough clue - it's about nuns. An unconventional comedy about a group of subversive sisters? It's perfect for Pedro, a firm believer in Luis Buñuel's anti-religious commentary, but Dark Habits is less harsh than you might expect.

Yolanda (Labyrinth of Passion's Cristina Sanchez Pascual) is a pop singer with a taste for hard drugs. When her boyfriend overdoses, the cops come looking for her. So she pulls a Whoopi Goldberg and hides out in a convent. But this is far from Sister Act, brother. These are some seriously whacked out nuns.

Yes, even more rock and roll than Maggie Smith.

Under the leadership of their oddball Mother Superior (Julieta Serrano), the nuns are encouraged to humble themselves to the point of humiliation. And so we have the brilliantly named Sister Damned (Carmen Maura), Sister Rat (Chus Lampreave) and, best of all, Sister Manure (the hilarious Marisa Paredes).

Running around in their penniless convent, they're struggling to stay open, which is terrible news for the ruined souls to whom they must offer refuge. Not that anyone's asking for help - Yolanda's their only guest. But that's just the way Mother Superior likes it, because she rather likes Yolanda. In a sexual, lesbigay kind of way. 

Singing the bolero together while shooting up heroin, the Mother Superior and Yolanda carry out their drugged-up love affair in secret. But the other nuns are hardly innocent. One of them bakes acid-flavour cakes while another writes trashy porn novels with titles like "Call of the Flesh". And in between the drug trafficking, distinctly non-spiritual hallucinations and the sewing of racy dresses to wear under their habits, Sister Damned looks a pet tiger while playing the bongos.

It all sounds like a typically barmy Almodóvar set-up, and it is, but much like What Have I Done to Deserve This?, the tone is closer to a serious melodrama than straight-out comedy. The humour is dark, but also notably lacking compared to the outrageousness of Labyrinth of Passion.

Dark Habits, then, could be seen as a disappointing third outing for the Spanish director, perhaps because it was his first studio-financed film. But while there may not be the farcical laughs of Almodóvar's stronger films, the anti-religious message is still fairly faithful to Luis Buñuel's work. 

At one point, Yolanda's make-up produces a mock Shroud of Turin for the Mother Superior to treasure. "It is in imperfect creatures that God finds all His Greatness," she says solemnly.

It's hardly the brazen rhetoric of Buñuel's Nazarín, but the nonsensical behaviour of the nuns in attempting to uphold their crumbling institution contained enough satire to make an impact in post-Franco society. So much so that Dark Habits was rejected by Cannes Film Festival for its sacrilegious content.

Looking back now, it's really not that scandalous or angry, but Dark Habits is an interesting piece to consider. It's a subtle comment on the structure of formal religion, but also a marked contrast to the bawdy urban humour of the Comedia Madrileña - proof that Almodóvar could produce more serious work after his vibrant, liberated first two movies.

Good Morning Freedom! - Spanish Cinema After Franco runs at the BFI until Thursday 7th July.