He finished his lunch and called Claude. He needed the man’s local knowledge.

‘Tree stumps,’ he said shortly. ‘How do they get rid of them round here?’

‘They dig them out, mostly,’ Claude replied. ‘The impatient ones dump petrol on them and let them burn out, but most just use muscle and do it the hard way, digging down through the roots or dragging them out with horses or a tractor. Why? You thinking of going into the land clearance business?’

‘Not me. How about the really impatient ones. What do they do?’

Claude hesitated. ‘You mean explosives, don’t you?’

‘Jesus.’ Rocco felt his spirits flag. Maybe Didier hadn’t been lying after all.

‘There’s the odd one uses dynamite,’ Claude confirmed with reluctance. ‘Put a stick under the root bowl and retire to a safe distance. Bam – problem solved.’

‘Where would they get it?’

‘There are one or two quarries in the region. Could be from them – I doubt their records are as reliable as they should be. Apart from that, I wouldn’t know. Who are you asking about?’

Rocco explained about his conversation with Didier. ‘If he did have plastic at his place, it does away with my theory that someone was trying to kill him.’

Claude made a soft noise over the line. ‘He’s lying. Think about it: that miserable cretin can lay his hand on more explosive material than the national armoury. Why would he need to risk buying dynamite from a dodgy source? Furthermore, he’s never blown any stumps out because he doesn’t need to clear the land. Only farmers do that.’

‘You sure?’

‘Positive. Any explosion on his land would be heard around the village – just like the one that blew off his hand. Ask anyone, they’ll tell you.’

Rocco had been suckered. Didier had taken advantage of him being new to the village to spin him a story, probably on the basis that, to a city cop, it sounded perfectly reasonable and not worth checking further.

‘What did he say about the photo?’ asked Claude.

‘That’s the odd thing. I don’t think he’d ever seen it before.’

‘Really? It was on the board in his house.’

‘I know. If he’s telling the truth, then someone else put it there – possibly the same person who tried to kill him. Unsettle him first by reminding him of the past … then bam.’

‘Christ, this is getting complicated. What next?’

‘We check and recheck our facts. Can you meet me down at the Blue Pool in twenty minutes? There’s something I want to look at.’

He went out to the car and saw Mme Denis on the other side of the hedge, hoeing her garden. She waved at him.

‘You seem very busy, Inspector,’ she said genially. ‘This place hasn’t seen such drama in years.’

‘Sorry about that,’ he replied. ‘I’ll try to get it under control as quickly as possible.’

She shrugged fatalistically. ‘Good luck with that. I’ve lived here long enough to know everyone and everything, and do you know what, Inspector? There are always surprises. Always.’

He nodded at this touch of philosophy and got in the car, then drove down to the marais. The village was quiet. He eyed the co-op as he passed through the square, but the windows reflected blankly back at him.

Parking on the turning circle near the big lodge, he put on his new boots. There was no sign of Claude yet, but that was fine: he wanted time by himself to think things through. As he made his way through the undergrowth to the Blue Pool, he felt clumsy in the unaccustomed footwear, but at least it kept out the water soaking the ground underfoot.

He circled the pool several paces back from the edge, studying the various directions of approach from the marais. It quickly became obvious that there were few options available, either because of impenetrable bushes or stretches of soft ground oozing with dangerous-looking mud. Even a heavy plank of wood, no doubt having once been used to negotiate a stretch of soft ground, was being absorbed gradually under its own weight.

He moved closer to the pool, narrowing down the most likely direction, then went round to the opposite side and knelt down, running his eye over the long grass on the far side to see if there were any telltale signs from this perspective. He could just about make out a dark, zigzag pattern showing through the undergrowth where someone had walked or run, but it was too close to where he and Claude had stood on their first visit to be certain.

A car engine disturbed the silence. He recognised the urgent whine of a 2CV, followed by the tinny slamming of a door. Moments later came the tramp of footsteps and Claude appeared.

Rocco bent back to his task. Then he felt a jolt. A clump of earth had been torn away from the edge of the pool on the far side, like a bite from a pie crust. It was too distinctive to be mistaken, but had he been on the other side, where Claude was now standing, it would have been hidden by the overhanging grass. He stood up and walked round until he reached the spot, beckoning Claude to come closer. He needed another set of eyes to witness this. The grass here was flattened, and when he bent over to examine the edge of the pool, he felt the familiar thrill of the hunter finding a clue.

‘See what you read from this.’ He stood aside to allow Claude to examine the spot, and ran his eyes over the surrounding area of undergrowth. He could almost picture the scene like a shot from a movie.

Nathalie Berbier must have run through the grass from the direction of the lodges, her path just about visible from the bent and broken stems. Too heavy and coarse to adjust themselves easily, they had browned and gone dry, leaving a faint but discernible trail. Unaware of the danger in her path, she had run straight towards the pool. Propelled by whatever forces were driving her, she had been unable to stop herself in time, and had plunged over the edge. The water soaking into her uniform and whatever drink or substances had been in her system would have done the rest.

‘Did she fall or was she pushed?’ murmured Claude, reading the situation.

‘I think she fell. If she was pushed, there would be signs of a struggle.’

He bent down alongside Claude and peered over the edge. As he had seen before, the sides were clear white with a blue tinge, curving gently like the inside of a giant cereal bowl, the surface smooth and unbroken all the way down to the dark funnel in the centre. He reached below the surface and dug his fingertips into the side, feeling a shiver worm its way down his back as they sank without resistance into the soft texture. There was no chance of anyone pulling themselves out with this stuff, especially a woman weighed down by wet clothing. He pulled out his hand and rubbed his fingers together.

Chalk. Soft and slimy. He wiped his hands on the grass and remembered the white substance on the dead woman’s shoes and what he’d taken as scuff marks on her uniform.

‘How did you arrive at this?’ Claude sounded faintly sceptical, but Rocco could tell he agreed with the scenario. ‘You had one quick look days ago.’

‘Random signs, that’s all.’ He explained about the fresh water in Nathalie Berbier’s lungs and stomach and the chalk marks on her shoes. ‘This is the only place where fresh water gathers. Anywhere else and her lungs and clothing would have been full of silt.’

‘Like the lakes.’

‘Exactly.’

‘I see. But how did the killer get her out without leaving more signs? She’d have been very heavy.’

Rocco led him to the other side of the pool to where he’d seen the discarded plank of wood. He had no proof of what he was thinking, but it seemed a logical explanation. ‘I once saw a river cop use a ladder to get a drunk out of the Seine. No way he could have lifted him, so he used leverage instead. The killer would have slid this under the body, then dragged her along the plank until he could lift her clear.’ He peered along the roughened wood and plucked a thread of dark cloth from the grain along one edge. ‘There. Minimal traces left behind and just possible for a strong man to do.’