'Thanks for the cases,' I told him. 'I couldn't have managed them.'

He paused to stare at me in his appraising way, neither sympathetic nor hostile. 'It's my job, Mr Sinclair.'

'It's not your job – but thanks. I had a small flying accident.'

'You broke your knees. That's tough.' He spoke with an American accent, but one learned in Europe, perhaps working as a security guard for a local subsidiary of Mobil or Exxon. 'You have a commercial licence?'

'Private. Or did have, until they took it away from me. I publish aviation books.'

'Now you'll have time to write one yourself. Some people might envy you.'

He stood with his back to the pool, the trembling light reflected in the beads of water on the holster of his pistol. He was strong but light-footed, with the lithe step of a professional dancer, a tango specialist who read Scott Fitzgerald and took out his frustrations on swimming pools. For a moment I saw a strange image of him washing his gun in the pool, rinsing away David Greenwood's blood.

'Keep flying speed…' He saluted and strode away. As he passed the pool he leaned over and spat into the water.

We sat on the terrace beneath the awning, listening to the gentle flap of canvas and the swish of lawn sprinklers from nearby gardens. Far below were the streets of Cannes, dominated by the twin domes of the Carlton Hotel, a nexus of noise and traffic that crowded the beach. The sun had moved beyond La Napoule and now lit the porphyry rocks of the Esterel, exposing valleys filled with lavender dust like the flats of a forgotten stage production. To the east, beyond Cap d'Antibes, the ziggurat apartment buildings of Marina Baie des Anges loomed larger than the Alpes-Maritimes, their immense curved facades glowing like a cauldron in the afternoon sun.

The swimming pool had calmed. Halder's glob of spit had almost dissolved, the sun-driven currents drawing it into a spiral like the milky arms of a nebula. An eager water spider straddled one of the whorls and was busy gorging itself.

Penrose's tour of the house had impressed Jane, who seemed stunned by the prospect of becoming the chatelaine of this imposing art-deco mansion. I hobbled after them as Penrose guided her around the kitchen, pointing out the ceramic hobs and the control panels with more dials than an airliner's cockpit.

In the study, virtually a self-contained office, Penrose demonstrated the computerized library, the telemetric links to hospitals in Cannes and Nice, and the databanks of medical records.

Sitting at the terminal, Jane accessed the X-rays of my knees now held in the clinic's files, along with an unforgiving description of my accident and a photograph of the ground-looped Harvard.

Tapping her teeth, Jane read the pathologist's analysis of the rogue infection that had kept me in my wheelchair for so many months.

'It's right up to date – practically tells us what we had for breakfast this morning. I could probably hack into David's files…'

I clasped her shoulders, proud of my spirited young wife. 'Jane, you'll tear the place apart. Thank God it doesn't say anything about my mind.'

'It will, dear, it will…'

Gazing at the garden, Jane finished her spritzer, eager to get back to the terminal.

'I'll give you a list of interesting restaurants,' Penrose told her. He sat by himself in the centre of the wicker sofa, arms outstretched in the pose of a Hindu holy man, surveying us in his amiable way. 'Tétou in Golfe-Juan does the best seafood. You can eat Graham Greene's favourite boudin at Chez Félix in Antibes. It's a shrine for men of action like you, Paul.'

' […] here. Absolutely perfect. So what went wrong?'

Penrose stared at me without replying, his smile growing and then fading like a dying star. His eyes closed and he seemed to slip into a shallow fugue, the warning aura before a petitmal seizure.

'Wilder…' Concerned for him, Jane raised her hand to hold his attention. 'Dr Penrose? Are you -?'

'Paul?' Alert again, Penrose turned to me. 'The aircraft, they're such a nuisance, I didn't quite catch what you were saying.'

'Something happened here.' I gestured towards the office buildings of the business park. 'Ten people were shot dead. Why did Greenwood do it?'

Penrose buttoned his linen jacket in an attempt to disguise his burly shoulders. He sat forward, speaking in a barely audible voice. 'To be honest, Paul, we've no idea. It's impossible to explain, and it damn near cost me my job. Those deaths have cast a huge shadow over Eden-Olympia. Seven very senior people were killed on May 28.'

'But why?'

'The big corporations would like to know.' Penrose raised his hands, warming them in the sun. 'Frankly, I can't tell them.'

'Was David unhappy?' Jane put down her glass. She watched Penrose as if he were a confused patient who had wandered into Casualty with a garbled tale of death and assassination.'We worked together at Guy's. He was a little high-minded, but his feet were on the ground.'

'Completely.' Penrose spoke with conviction. 'He loved it here – his work at the clinic, the children's refuge at La Bocca. The kids adored him. Mostly orphans abandoned by their north African and pied-noir families. They'd never met anyone like David. He helped out at a methadone project in Mandelieu…'

Jane stared into her empty glass. The sticky bowl had trapped a small insect. 'Did he ever relax? It sounds as if the poor man was overworked.'

'No.' Penrose closed his eyes again. He moved his head, searching the planetarium inside his skull for a glimmer of light. 'He was taking Arabic and Spanish classes so he could talk to the children at the refuge. I never saw him under any stress.'

'Too many antidepressants?'

'Not prescribed by me. The autopsy showed nothing. No LSD, none of the wilder amphetamines. The poor fellow's bloodstream was practically placental.'

'Was he married?' I asked. 'A wife would have known something was brewing.'

'I wish he had been married. He did have an affair with someone in the property-services division.'

'Man or woman?'

'Woman. It must have been.' Jane spoke almost too briskly. 'He certainly wasn't homosexual. Did she have anything to say?'

'Nothing. Their affair had been over for months. Sadly, some things are fated to remain mysteries for ever.'

Penrose scowled at the pool, and chewed on a thumbnail. The garden was now in shadow as the late-afternoon light left the valley of Eden-Olympia, and the top floors of the office buildings caught the sun, floating above the trees like airborne caravels. Our conversation had drained the colour from Penrose's face. Only his hands continued to move. Resting on the cushions beside him, they flinched and trembled with a life of their own.

'Was anyone else involved?' I pointed towards Cannes. 'Co-conspirators on the outside?'

'The investigating magistrate found nothing. He spent weeks here with his police teams, staging reconstructions of the murders. A strange kind of street theatre, you'd think Eden-Olympia was taking over from the Edinburgh Festival. Meanwhile, foreign governments were pressing hard for a result. Half the world's psychologists jammed the baggage carousels at Nice Airport. There was even a televised debate in the conference room at the Noga Hilton. They came up with nothing.'

'He tried to kill you.' Jane pushed her glass away, distracted by the insect's angry buzzing. 'You were wounded. How did he look when he shot you?'

Penrose sighed, his heavy chest deflating at the memory. 'I didn't see him, thank heavens. I'm not sure that I was one of his targets. A glass door blew in while I was checking something in the pharmacy. David was firing from the outside corridor at Professor Berthoud. By the time I stopped bleeding he'd gone.'

'Grim…' I felt a sudden sympathy for Penrose. 'A nightmare for you.'