The Location Hunters: A look that lingers in the Venice mist: In dark alleys off the Grand Canal, Frank Barrett rediscovers the sinister beauty of Nic Roeg's film, Don't Look Now

The woman in the video shop cast an expert eye over my rentals record card. 'You've got a thing about Don't Look Now. This is the eighth time you've taken it out. You, er . . . um . . . must like it,' she said.

The er . . . um was well judged. In the research for this feature, Don't Look Now had become something of a dangerous obsession. I practically wore the heads out on my video player, running the tape back and forth to pinpoint the film's locations - slowing the motion and freezing the frame in the hope of reading the faint names on the street signs.

I thought I had worked out where the main places in the film were, but when I actually went to Venice and tried to locate them , even though I walked and rewalked the streets (or what amount to streets in Venice), some of the major scenes continued to elude me.

On my return, I managed to speak to the film's director, Nic Roeg, who generously filled in the gaps. I also faxed Julie Christie, who rang me (and left the sort of message on my answering machine you can only dream about: 'Frank, this is Julie Christie. Could you ring me?')

After more research, I reached the conclusion that I had to go back to Venice just one more time. Yes, I had a thing about Don't Look Now.

The fact that the film hasn't taken its proper place in the list of all-time British classics is largely, I believe, the result of unfortunate timing. In autumn 1973, everybody was talking about The Exorcist, that famously vomit-spattered account of the demonic possession of a young girl played by Linda Blair. The controversy whipped up by the sight of Blair's head revolving on her shoulders, and by a scene involving the indecorous use of a crucifix, overshadowed the release of Don't Look Now.

Don't Look Now was a film with an horrific ending, but it was no gothic Hammer horror. It was perhaps this that confused the critics, who found it difficult to categorise this extraordinary movie.

It was based on a Daphne du Maurier short story (she had written two of Hitchcock's greatest successes, Rebecca and The Birds); it was directed by Roeg (whose two previous films had been the well-regarded Performance and Walkabout); and it starred Julie Christie and Donald Sutherland, both at the height of their box-office success. But its deftly constructed plot, which built to one of the most terrifying endings ever seen in a film, proved no match at the box office for the less subtle terrors of The Exorcist.

Looking back over 20 years, I can barely remember the grotesque set-pieces of The Exorcist. Those final moments of Don't Look Now, however, are firmly etched in my mind. The ghastly figure in the shiny red coat, the knife, the oozing blood, the dying Donald Sutherland character - his leg twitching as it kicks out and smashes the window. 'Ah, yes,' says Roeg recalling the moment with obvious satisfaction, 'I got that from the news footage of the assassination of Robert Kennedy. I remembered that moment when he was lying on the floor, dying, his leg jerking . . .'

'Don't look now, but . . .' was a favourite saying of the du Maurier family. According to her biographer, Margaret Forster, Daphne took a particular delight in observing the eccentricities and curiosities of fellow diners in a restaurant and relaying them, sotto voce, to her husband and children. To give a 1970 short story the title 'Don't Look Now' (and to use the phrase in the opening line) was therefore a jeu d'esprit the whole du Maurier family would have enjoyed.

From its striking beginning ('Don't look now,' John said to his wife, 'but there are a couple of old girls two tables away who are trying to hypnotise me'), to the terrifying twist - revealed in the third to last paragraph - Don't Look Now is a finely crafted piece of writing.

The main elements of the story, set in an out-of-season Venice, were all observed by du Maurier on her visits to the city. She had seen two sisters, one of them blind, and she had seen what she thought was a little girl in a coat with a pixie hood - the misapprehension that provides the awful twist in the tale.

The plot hinges on a series of episodes linked with clairvoyance and psychic precognition - subjects that fascinated du Maurier throughout her life. John Baxter and his wife Laura take a holiday in Venice following the death of their young daughter. In a restaurant they meet two elderly Scottish sisters, one of them blind and clairvoyant, who tells Laura that she has seen her dead daughter sitting at the restaurant between her and John, smiling and happy. (The blind sister also reveals that the daughter is warning John and Laura not to stay in Venice because their lives are in danger there.)

John is sceptical, but the news that their daughter is happy lifts Laura's depression. They return to their hotel and make love for the first time since their daughter's death (the explicitness of this scene - perhaps the most erotic sex scene with a married couple ever filmed - earned the movie some small coverage in the tabloid press).

When Laura has to fly home unexpectedly to be with their sick son, John is left alone in Venice. But later that day, riding in a water ferry down the Grand Canal, he passes another boat on which he sees Laura with the two sisters (this, we later realise, is a moment of precognition).

Confused, he returns to the hotel but cannot not find Laura and, believing she has fallen under the influence of the sisters, reports her disappearance to the police, whose resources are already overstretched in the hunt for a vicious murderer.

To his surprise John receives a telephone call from Laura in England who says that all is well with their son. Relieved, John believes the problems are over. But, of course, they have only just begun.

In his film version - which was shot almost wholly on location in Venice - Roeg and the scriptwriters took this basic plot and embellished it with neat touches. For example, John becomes an atheist church restorer employed by a Venetian bishop. In the du Maurier story, the daughter had died of meningitis; in the film, we see her drown at the very beginning in the pond of an English back garden. The menace of water has disturbing resonances later in the canals of Venice.

Don't Look Now is that very rare phenomenon: a good piece of fiction which became an even better film.

'Venice is like a city in aspic,' says the blind, clairvoyant sister in Don't Look Now. 'My sister hates it. She says it's . . . like after a dinner party, and all the guests are dead and gone . . . Too many shadows . . .'

The Venice revealed in Don't Look Now is a very different city from the one the visitor sees, Julie Christie told me. 'It had that strange, ghostly emptiness you see in the picture, full of magic and portent, very wet walls, dark alleyways that were damp and glistening. And continual reflections; everywhere you looked there was water.'

Nic Roeg was anxious to show a different side to the city familiar from tourist posters and picture postcards ('St Mark's Square is not the city of Venice'). In fact St Mark's Square makes just one fleeting, easy-to-miss appearance; the rest of the film sticks resolutely to the backways.

'Venice is a wonderful thing, a work of art which reveals itself slowly, as do all great beauties,' said Roeg. 'And, of course, beauty has its sinister side. For example, one of the strange things about walking in Venice is that you can hear people but you don't see them.'

Roeg exactly captured this spirit of out-of-season Venice: people in hats and coats, pigeons flapping away out of the deserted squares as walkers approach, the peculiar luminescence of the winter sunlight, dozing cats. He also captures the distinctive sounds: an unseen piano-playing, the peremptory parp] of the boat horns and the sound of their engines, particularly the special whirr of the vaporetto coming into berth as it throws its engine into reverse and its hull crunches against the pier. (In the film the blind sister says that she loves Venice for its sounds.)

Don't Look Now was filmed in January and February. 'Venice was empty. I loved that,' said Roeg. 'You really got a chance to be part of a city. It's one of my favourite places but I feel that really it is a most beautiful prison: when you walk you just go round in circles, trapped.'

In following the Don't Look Now trail, you will, I hope, not get trapped - but you will almost certainly get lost: a good city map is essential.

Start at the Hotel Gabrielli Sandwirth on the Riva degli Schiavoni, a few minutes' walk to the east along the waterfront from St Mark's Square. The lobby played the part of the 'Europa Hotel' where John and Laura Baxter stayed.

The owner of the hotel is Heidi Perkhofer, a charming old lady of Austrian descent. She remembers the filming very clearly: 'Julie Christie was very nice, very kind. They changed the lobby of the hotel all around, they put the entrance here - all for the story.' Did she like the film? 'I've never seen the film, I never go to the cinema,' she admitted, regretfully.

There wasn't enough space in the Gabrielli's rooms to film the interiors. These scenes, including the famous love scene, were filmed in a suite in the Bauer Grunwald, which is on the west side of St Mark's Square.

From Schiavoni you can take a No 2 ferry to Zattere. From here it is a short walk to the 12th-century church of San Nicolo dei Mendicoli, which in the film is being restored by John (the church was really restored by the British Venice in Peril fund with work beginning in 1973). The mosaic that John studies by climbing up scaffolding (in which act, in a memorable slow-motion sequence, he nearly falls to his death), was specially made by local students for the film and is not to be seen in the church.

The San Polo area, north-east of San Nicolo, is one of the quietest and most charming parts of Venice. Search out the Ponte Vinanti and the lovely Calle Castelforte, near San Rocco church, where John is shown walking while being shadowed by the detective.

Follow the signs to the 'Ferrovia' which will take you to the Scalzi bridge. Stand on the bridge looking down the Grand Canal towards St Mark's; the landing stage to your immediate left is where we see Laura being carried from the restaurant on her way to the water ambulance after fainting (and bringing everything on the table crashing down on to the marble floor).

I wandered into the Ristorante Roma, next to this landing stage, to see if the interior matched the inside of the restaurant shown on the film. Peering into a now-disused room that most closely matched the film's restaurant, I incurred the wrath of a waiter who bore an uncanny resemblance to Mussolini. I told him I was just looking. 'Just looking? Just looking?' He imitated me wandering around. 'Up and down, up and down,' he moaned. When I told him I wanted to order a meal, his attitude abruptly changed. He gave me an horrendous death's-head grin (but continued to mutter what sounded like obscenities under his breath as he served the food).

It's a pleasant 25-minute walk from here down to the La Fenice opera house (it's worth taking a short detour for a look at the Ghetto, the old Jewish district): if you're pushed for time, hop on a vaporetto to the Accademia bridge (en route you will pass, on your right, the church of San Stae where the film ends with the funeral procession).

The Hotel La Fenice at the back of the opera house is where the two sisters are staying at the close of the film. This is where John Baxter returns with the blind sister after bringing her from the police station. The hotel's owner also has vivid memories of Julie Christie: 'Yes, yes, out there on the step. Julie Christie was there]'

In the film, John seems to take just a couple of minutes to walk from the Hotel La Fenice to the location of the final moments of the action. In reality the Calle di Mezzo, just below the Campo Santa Maria Formosa - with its gorgeous mildewed wedding-cake church - is at least a 15-minute walk away. It is here that John catches sight of the figure in the pixie hood who slips through a large iron gate before disappearing up some stairs. The gate is now locked: the Griman Palace to which it belongs looks derelict and sad. Even if I could have crossed the canal to the gate, the haunting memory of the film's ending is so vivid I certainly wouldn't have had the nerve to enter.

Christie's visit to Venice to shoot the film was her first and - so far - last trip to La Serenissima. 'I had never been before, and I've never been since. So I've never seen tourist Venice. The whole thing was such a wonderful experience I've never really dared to go back.' And her opinion of the film? 'I haven't seen it for ages, but I always thought it was a good film, one of Nic's best. It was visually fantastic.'

Roeg, who has just completed work on his latest film, Conrad's Heart of Darkness, takes a more pragmatic attitude. 'I hope it worked. Making films involves so much argy bargy that they are often difficult to remember with pleasure. Making a film is just part of life: it's gone . . . just part of life . . .'

Shortly before the film opened, Daphne du Maurier was given a special preview in London and expressed her delight. She had not, however, seen the whole picture. Anxious that it would cause her offence, her family had advised the film company - just for the special showing - to edit out the full and frank sex scene. Even by the homicidal knife-wielding standards of Don't Look Now, this was perhaps the unkindest cut of all.

(Photographs omitted)