I leaned against the harbour wall, surrounded by people who had carried their drinks from the nearby bars. Together we waited for the speedboat to disappear into one of a hundred bays along the coast, before slipping under the cover of night into a marina at Fuengirola or Benalmadena.

But the thief had still to satisfy his appetite for play. A game of tease and chase began in the open water three hundred yards from the mole. The cruiser swerved after the circling speedboat, which leapt nimbly past its pointed bows like a torero evading an overweight bull. Wallowing in the churned water, the cruiser's captains searched the criss-crossing wakes, their lights sweeping the confused waves. The speedboat's engines were silent, as if the thief had at last tired of his game and was about to slip into the shadows of the Estrella peninsula.

I decided to turn away when a blaze of orange fire lit up the sea, exposing a thousand wave-crests and the passengers standing on the foredeck of the cruiser. The speedboat was burning, its engines still pushing it through the water. In the moments before it sank, bows following the heavy outboards into the deep, a last explosion tore apart its fuel tank and bathed the marina and the watching crowds in a copper halo.

I looked down at my hands, which flared at me in the darkness. The harbour road was packed with cheering spectators who had stepped from the nightclubs and restaurants to enjoy the display, eyes gleaming like their summer jewellery. Arm-in-arm, a cheerful couple swayed past me into the path of a passing car. As it edged by them the man slapped its roof with his hand. Alarmed, the driver looked over her shoulder, and through the confused air I saw Paula Hamilton's anxious face.

'Paula!' I shouted. 'Wait for me… park by the boatyard.'

Had she come to look for me, or had I read her features into those of another driver? The car moved through the crowd, then left the harbour and joined the lower corniche road to Fuengirola. Half a mile away, below the ruins of a Moorish watch-tower, it stopped beside the breaking waves, its lights fading in the darkness.

The cabin-cruiser circled the floating debris of the speedboat, its crew hunting the waves. I assumed that the thief would be swimming towards the rocks below the watch-tower, to a rendezvous previously arranged with the car's driver, who waited for him like a chauffeur outside a stage-door after the evening's performance.

Crime at Estrella de mar had become one of the performance arts. As I drove David Hennessy from the Club Nautico to the harbour, the curving hillside above the town resembled an amphitheatre warmed by the morning sun. Residents sat on their balconies, some with binoculars, watching the Guardia Civil salvage launch drag the remains of the stolen speedboat into the shallows below the corniche road.

'Frogmen…?' Hennessy pointed to the goggled black heads moving among the waves. 'The police are taking it all very seriously.'

'They're under the impression that a crime has been committed.'

'Hasn't it? Charles…?'

'It was a piece of night-theatre, a water-borne spectacular to perk up the restaurant trade. A party of Middle East tourists played the clowns, with a chorus line of French good-time girls. Brutal, but great fun.'

'I'm glad to hear it.' Eyebrows raised, Hennessy tightened his seatbelt. 'And who played the villain? Or the hero, I should say?'

'I'm not sure yet. It was quite a performance – we all admired his style. Now, where exactly is Sansom's cottage?'

'In the old town above the harbour. Take the Calle Molina and I'll show you the turn-off. It's an unexpected side of Estrella de Mar.'

'Unexpected? The place is a set of Chinese boxes. You can go on opening them to infinity…'

Hennessy was closing Sansom's house, packing up his possessions before freighting them back to his cousins in Bristol. I was curious to see this weekend retreat, presumably the love-nest where Sansom had entertained Alice Hollinger. But I was still thinking of the speedboat thief playing his games with the cabin-cruiser. I remembered the eager eyes of the people emerging from the nightclubs along the quay, flushed by more than the copper sun of the exploding fuel tank.

We drove around the Plaza Iglesias, packed with residents drinking their morning espressos over copies of the Herald Tribune and the Financial Times. Scanning the headlines, I commented: 'The rest of the world seems a long way off. The scene last night was bizarre, I wish I'd filmed it. The whole waterfront came to life. People were sexually charged, like spectators after a bloody bull-fight.'

'Sexually charged? My dear chap, I'll take Betty down there tonight. She's obviously spent too much time with her water-colours and flower-arranging.'

'It was a show, David. Whoever stole the speedboat was putting on a performance. Someone with a taste for fire…'

'I dare say. But don't read too much into it. Boats are stolen all the time along the coast. Estrella de Mar is remarkably free from crime, compared to Marbella and Fuengirola.'

'That's not strictly true. In fact, there's a great deal of crime in Estrella de Mar, but of a unique kind. It seems unconnected, but I'm trying to piece it all together.'

'Well, let me know when you do. Cabrera will be glad of your help.' Hennessy guided me into the Calle Molina. 'How's the investigation going? You've heard from Frank?'

'I talked to Danvila this morning. There's a chance Frank may agree to see me.'

'Good. At last he's coming to his senses.' Hennessy was watching me obliquely, as if trying to read my thoughts through the sides of my eyes. 'Do you think he'll change his plea? If he's ready to see you…'

'It's too early to say. He may feel lonely, or realize how many doors are about to shut on him.'

I turned off the Calle Molina into a narrow roadway, one of the few nineteenth-century streets in Estrella de Mar, a terrace of renovated fishermen's cottages that ran behind the restaurants and bars of the Paseo Maritimo. The once modest dwellings in the cobbled street had been tastefully bijouized, the ancient walls pierced by air-conditioning vents and security alarms.

Sansom's house, painted a dove-egg blue, stood on a corner where the terrace was divided by a side-street. Lace curtains veiled the kitchen windows, but I could see lacquered beams and horse brasses, a ceramic hob and an antique stone sink with oak draining board. Beyond the inner windows lay a miniature garden like a powder-puff. Already I could sense the freedom that this intimate world would have given to Alice Hollinger after the vastness of the mansion on the hill.

'You'll come in?' Hennessy heaved himself from the car. 'There's some decent Scotch that needs to be finished.'

'Well… a few drinks always make the car go better. Have you found any of Alice Hollinger's things?'

'No. Why on earth should I? Have a look round. You'll find it interesting.'

While Hennessy unlocked the front door I worked the wrought-iron bell-push, eliciting a few bars of Satie from the electronic annunciator. I followed Hennessy into the sitting room, a chintzy arbour of fluffy rugs and elegant lampshades. Packing chests stood on the floor, partly filled with shoes, walking-sticks and expensive leather shaving tackle. Half a dozen suits lay on the settee, next to a pile of monogrammed silk shirts.

'I'm sending all this stuff to the cousins,' Hennessy told me. 'Not much to remember the fellow by, a few suits and ties. Decent chap-he was very formal up on the hill, but when he came here he changed into another personality, rather blithe and carefree.'

Beyond the sitting room was a dining alcove with a small blackwood table and chairs. I imagined Sansom having two lives, a formal one with the Hollingers and a second down here in this doll's-house of a cottage, furnished as a second boudoir for Alice Hollinger. Her husband's discovery of the affair might have released an anger strong enough to consume the entire mansion. The notion of Hollinger committing suicide had never occurred to me, a Wagnerian immolation that might have appealed to a film producer, he and his unfaithful wife dying with their lovers in a gigantic conflagration.