Tony felt a faint surge of excitement. It might not seem much but, at this stage of an investigation, any deviation from the pattern carried potentially huge significance. And in this instance, it could be all the more important because this was the crime that had been interrupted. Under the stress provoked by that intrusion, Geronimo might have let his guard slip enough to provide a chink in his boilerplate security system.

He was in a fever of impatience to pick up his laptop and get back to Petra’s. Of course, the taxi from Tempelhof seemed to take forever, finding every traffic hold-up in central Berlin. He let himself into the empty flat and made straight for the study and Petra’s scanner. While he was waiting for his computer to ready itself, he took out the magnifying glass from his laptop case and studied the picture more closely. He went back through to the dining area and pulled out the other crime scene photographs. A few minutes with the magnifying glass and his heart rejoiced. He’d been right. All the knots on the ligatures appeared to be straightforward, common or garden reef knots, apart from the single exception in that one crucial Bremen photograph.

He returned to the study and plugged the scanner into his laptop’s USB port. Minutes later, he was looking at an enlarged and enhanced section of the key picture. Tony knew nothing about knots, only that this one was different from the others. He connected to the internet and linked to a search engine, typing in <knots>. Within seconds, he had a list of websites devoted to the craft of knot-tying. The first site he tried offered him a link to an on-line newsgroup of knot enthusiasts. Tony logged on to the newsgroup and posted a message:

I’m a knot ignoramus, and I need some help in identifying a knot from a photograph, also info on where it’s likely to be used and by whom. Is there anyone out there that I can send the pic to as a JPEG file?

It would take at least a few minutes to get a response, always supposing there was a knot anorak on-line at this precise moment. To calm his urgent excitement, Tony went through to the kitchen and made himself a pot of coffee. For the first time in hours, he wondered how Carol was getting on. He remembered their tentative arrangement to meet at some point, but he didn’t know when he would be able to get away now he had the bit between his teeth.

When he got back to the desk, he sent her an e-mail, suggesting they meet later that evening. There was a message in his in-box from someone who signed himself Monkey’s Fist. Tony knew enough to recognize the name of a particular knot, and he opened the message with a glimmer of hope.