They drank their coffee and mulled over possible locations for the hideaway. ‘There were three places I couldn’t get to from the sea bank,’ Marie said, sipping her drink. ‘None looked particularly promising when I checked the satellite pictures, certainly none worth getting the drone up for.’

‘Andy only thought it was in the direction of Stone Quay. Maybe he was wrong. It could be anywhere.’ Jackman stared up at the wall map of the Fens. ‘The place is a maze of waterways. I’ve often had fantasies of owning a little cabin somewhere among the tiny creeks and lagoons, where I could watch wildfowl from dawn to dusk.’

Marie was slightly surprised at that. He lived in a sleepy village as it was, pretty well out in the countryside. But on reflection she understood what he meant. There were times when you needed to leave the police force parked up and be somewhere you weren’t liable to be called out at any time of day or night. A cabin out in that water-world would be ideal.

She jumped. Jackman’s mobile phone was ringing.

Dr Bourne’s measured tones filled the office on loudspeaker. ‘Christopher has told Jim everything he remembers. I hope it helps you. Do you have a pen handy?’

‘Yes, yes, ready,’ snapped Jackman.

‘They did call it the Hideaway. To reach it, they drove past the marina, then turned off and took the long, straight road towards the sea bank and the old bird reserve at Stone Quay. At the T-junction they took the lane to the right and veered away from the river. He wasn’t sure about the exact directions at that point but mentioned passing a sluice where he had seen a grey heron in the water. Just after that, another lane heads down to the marsh. The Hideaway was on a creek that led back into the tidal river and was quite close to the estuary.’ Bourne took a breath. ‘And that’s all he remembers.’

‘How did he cope with being questioned?’ asked Jackman tentatively.

‘Apparently, it was quite strange,’ said Bourne. ‘For days, Christopher has been going on about wanting to see his father. Jim said that if he’d been a fanciful man, he would have said the boy sensed something was wrong. He’s been kept away from the media reports, so it couldn’t have been that. Anyway, talking about a happy time he’d shared with his father didn’t stress the boy out at all.’

Jackman thanked the doctor and went immediately to the wall map. ‘Do you know this spot, Marie? I don’t.’