Part of her wished she was out there in the field with him, but her own operation was sufficiently demanding and exciting to make that no more than a mild nag. For now, she was happy to leave him to his own devices, secure in the knowledge that when the decks were cleared, the world would be a different place for both of them.

Marijke had escaped from the mountain of paperwork in the office and headed over to Pieter de Groot’s canalside house. She was responding to a call from Hartmut Karpf in Köln, whose search team had found something curious when they’d combed Marie-Thérèse Calvet’s filing cabinet. It didn’t actually take the investigation much further forward, but she had a feeling Tony would be very, very interested.

It also had the advantage of getting her away from the glowering scowls of her team, whom she’d set the task of trying to establish every inland shipping vessel that had been within a fifty-kilometre radius of Leiden on the day of de Groot’s murder. She hoped her German colleagues were being as assiduous, so they could compare results. Otherwise, the exercise would be a complete waste of time. If they found any correlations, then the Germans could see if any of the bargees also owned a dark-coloured Golf. With a lot of luck and persistence, they might just come up with enough suspects for Tony’s profile to be genuinely useful.

She’d also sent one of her detectives off to the university library to see if he could find any letters or articles critical of the work of Pieter de Groot and the other victims. She had even less confidence that this wild idea of Carol’s would produce a worthwhile result, but she was determined to leave no avenue unexplored, no theory unexamined.

Marijke had to admit she felt disappointed with what they’d achieved so far. Sure, she knew profilers weren’t miracle workers, but she’d hoped for something more concrete than Tony had been able to give them. Maybe they’d been hoping for too much. It looked as if the only way these cases were ever going to be solved was by traditional, plodding police work. It wasn’t glamorous, but it sometimes got results.

It felt strange to be back in Pieter de Groot’s study. There were few traces of what had happened there. Just a watermark on the polished surface of the desk and a few traces of fingerprint powder where the technicians hadn’t cleared up properly after themselves. Maartens wouldn’t like that, she thought irrelevantly. He hated it when the SOCOs left a crime scene in a worse mess than they’d found it.