In Peter Biskind’s book Easy Riders, Raging Bulls, director William Friedkin recalls the first time he saw The Conversation, at a special screening at Francis Ford Coppola’s home in Napa Valley. “I thought it was like watching paint dry or listening to hair grow,” he grumbled. Friedkin’s verdict is manifestly unfair but easy to understand. Coppola, then Friedkin’s business partner in the short-lived Directors’ Company, had just made The Godfather and was about to make The Godfather Part II. For reasons which Friedkin and others found unfathomable, he took time out between these twin triumphs to write and direct a determinedly hermetic story about a surveillance expert (Gene Hackman) who thinks he may have stumbled on a murder plot.

This was as close to European arthouse as any Hollywood studio had been. Coppola, never shy about making lofty claims for his own work, suggested it was inspired by Herman Hesse’s Steppenwolf, cubist art, Hitchcock thrillers and Antonioni’s Blow-Up. He began the script in the mid-’60s, abandoned it because he thought it was terrible, but picked it up again once the unexpected success of The Godfather made him bankable.

Thanks to Watergate, The Conversation had a topical resonance for American audiences. The parallels with Nixon extend beyond simply the idea of covert taping: they’re there in the very fibre of the movie. Nixon was known as a private and defensive man, and Hackman’s Harry Caul is cut from similar cloth. His name may have been the result of a typing error by the secretary Coppola had hired to transcribe the screenplay, but it’s apt all the same. A caul is the portion of the amniotic sac that sometimes covers a child’s head at birth. It’s also a form of protective head gear, like a cap. Harry Caul (who started life as Harry Call) has his own outfit which makes him anonymous?a battered old mackintosh.

From the perspective of the audience, there’s a sense of uncomfortable complicity. We’re being invited to listen in and observe a man whose job is listening in on and observing others. (This release, with its audio tracks in which Coppola and lauded sound editor Walter Murch discuss the movie, adds yet another layer of self-reflexivity.) Despite Friedkin’s sardonic remarks about hearing hair grow, this is an utterly absorbing character study. From the very first shot?a high camera swoops down on a young couple in Union Square whom Caul is following for a mysterious businessman (Robert Duvall)?the craftsmanship is truly breathtaking. Bill Butler (who took over as cinematographer from Haskell Wexler once shooting had already begun) captures wonderfully forlorn images of Caul lost and adrift in the big city.

“What a stupid conversation! What the hell are they talking about anyway?” Caul’s assistant Stan (John Cazale) grumbles when he’s made to listen to the same tape for the umpteenth time. For Caul himself, though, the tapes have an almost religious significance, seem to contain some deeper truth.

In the early scenes, Coppola goes out of his way to portray Caul as paranoid. In one of the film’s most ironic and poignant scenes, we see him getting angry because the building supervisor has left a bottle of wine in his apartment to mark his birthday. How do people know it’s his birthday? How did the wine get into the apartment? He’s obsessed with breaching other people’s privacy but intent on preserving his own. “The one surefire rule I’ve learnt in this business is that I don’t know anything about human nature,” Caul remarks. The person he understands least is himself, but the more he pores over this one seemingly banal conversation between two lovers in a public square, the more vulnerable he becomes.

Coppola, by his own confession, was still a young and insecure film-maker when he made The Conversation. And it wasn’t a happy shoot. The director was so frustrated that he wrapped four days early, before he’d completed his own script, and left Walter Murch to pick up the slack.

Its troubled gestation shouldn’t blind anyone to its qualities. Friedkin’s barbs aside, this ranks with Coppola’s very finest work.