‘So, it was all about a bird,’ Perez continued as if the exchange between them had never occurred. ‘Slender-billed curlew. Some scientists thought it was extinct. You wouldn’t think it could generate so much passion. But I watched the birdwatchers come into Fair Isle for an American swan and I saw how mad they could be. Some of them almost in tears when they realized they could have missed it. And for Fowler it wasn’t just a hobby. It was his work. It was about respect, proving himself worthy of his job in journalism.’

‘So he found this curlew before Angela Moore did, but she claimed the credit.’ Rhona looked at her watch. Her sympathy hadn’t lasted for long. Perez thought the Fiscal just wanted the facts; she’d never been much interested in the background. That’s what social workers were invented for, Jimmy.

‘He worked out where he thought the birds might be breeding,’ said Perez. ‘Something to do with the insects they feed on. He looked at the maps, sought out likely search areas. They call it ground-truthing.’ Perez had liked the idea of ground-truthing when he’d heard about it, thought it was a useful concept in policing. It was about testing theories, keeping it real. Now he wondered how it could have excited him; it was an irrelevance.

‘It must have been galling for him to miss out on the credit,’ Laing said, showing some understanding at last. She would understand about professional jealousy. Perez had never met anyone quite so ambitious. ‘The woman became a real celebrity as a result of that book.’

‘Of course.’ Perez imagined Fowler trying to keep his business afloat, but everywhere he was hearing of Angela Moore’s success, while he scratched a living taking orders for books over the Internet, meeting up with the occasional eccentric in his shop. ‘Angela was on the television every five minutes, warden of Fair Isle, the most prestigious field centre in the UK. Of course it ate away at him. That should have been him. He woke up thinking about it and he dreamed about it at night.’

Rhona raised her eyebrows. Perhaps she was thinking that Perez knew something about obsession. He must wake up thinking about Fran dying in the dark on Fair Isle and no doubt he dreamed about it too.

‘Did the wife know what was going on? I still haven’t decided how we should charge her.’