St Paul’s Labyrinth. Jeroen Windmeijer

that walking away had been a bad idea. He’d been so taken aback by the strange encounter with Raven, the messages, and Arnold’s disappearance that he’d wanted to go off and investigate on his own. But where would he start?

      He went back to his office and took the folder from that afternoon’s lecture out of his bag. The students were required to turn up for least eighty percent of their lectures and he was required to keep accurate records of their attendance. Reading out a roll and ticking off every name individually took much too long, so he usually passed the register around the class. Of course, this sometimes meant that there were more people present on paper than were actually in the lecture hall. He usually brushed it off with a joke. (‘Once again, it appears that, just like a Russian election, we have more votes than voters.’)

      He ran his finger down the list of names, trying to remember their faces. He only succeeded in one or two cases. He soon realised that this was utterly useless. What had he hoped to find? A student called Raven Ravensbergen? Or a red arrow pointing to a name and the words ‘hora est’?

      He grumpily folded the list up again. As he slotted it back into the folder, his eye fell on the little book that he had been using on the course. More of a thick pamphlet than a book, its cover was printed on the same paper as the contents. Written on the front were the words: GEDEMPTEGRACHTENWANDELING or A WALKING TOUR OF INVISIBLE CANALS, published by the Leiden Canal Society and the Old Leiden Historical Society. It was a route around all the canals in Leiden that had been covered over or filled in.

      He picked it up distractedly. How was it possible that the tunnel had never been discovered before?

      He spread it open and began to read random pages, looking for answers.

      Leiden has always been a city rich with water. Around the middle of the sixteenth century, the Italian-Flemish merchant Guicciardini described the city as a true archipelago. He counted thirty-one islands, connected by a hundred and forty-five bridges. At that time, the city was still medieval in scale.

      He read on.

      And even now, one is struck by the abundance of water in Leiden. Over the years, however, many of the canals have been infilled or overvaulted. This walking tour hopes to give an impression of these changes. The route covers more than thirty sites where the city’s canals have been removed over the centuries, showing how the water gradually disappeared from Leiden.

      How the water gradually disappeared from Leiden …

      In the medieval city, the streets of Leiden became densely populated and, over the course of the seventeenth century, the city was expanded three times. The increased density of the buildings resulted in an increase in traffic on the streets. This was not only accommodated by the infilling of some canals, but primarily by means of moving them underground to large brickwork drainage channels, or by roofing the canals over.

      The tunnel they had discovered that afternoon was so far underground that it even ran below the canals that had existed in the Middle Ages. Peter leafed through the pamphlet looking for the illustration that showed all the city’s former canals.

      A few years ago, the invisible canals tour had been complemented by the addition of an urban legends walking tour that Peter and Judith had once taken. The tour guide had told them a story about each location they’d stopped at and asked the participants to guess whether or not it was true. There was a tale about the well in the Burcht that the guide had told them was false. In the seventieth century, it was believed that a tunnel started at the bottom of this well and led all the way to the ‘Roman arcenal near Cat-wijck’, as the contemporary sources put it. The tunnel was thought to have been built during the Spanish siege of the city in 1573–1574. According to the legend, a live herring was found in the well which was supposed to prove that it was connected to the coast. That fishy tale could obviously be disregarded as belonging to the realm of fables, but persistent rumours about the tunnels were widely accepted to be true.

      Then there was Annie’s Verjaardag, the café in the old city vaults which everyone ‘knew’ were part of an underground network of tunnels that led to the Burcht. The city had developed so densely around these areas that there had never been a serious attempt to find out how much truth there really was in the old stories.

      Although Peter knew a great deal about the history of Leiden, he hadn’t managed to make a correct guess about even half of the stories on the tour. The lesson he had taken away from the experience was: if a story sounded too unlikely to be true, then it probably was true.

      He ran his finger over the Nieuwstraat, another ‘invisible’ canal. He squinted at the page until the fine outlines of the buildings faded away and all he could see were the red and blue delineations that formed an alternative map of the city.

      He tapped his finger on the picture.

      If there had been a tunnel present ab urbe condita, he thought, then perhaps there wouldn’t have been much digging needed to connect it to the roofed-over canals … What if it wasn’t just one tunnel, but a whole labyrinth of tunnels beneath the city? My god, this could be one of the greatest archaeological discoveries of the century …

      He put the book down and picked up the new mobile phone again. The only apps on it were the pre-installed programs it would have been sold with, and Wickr. Tomorrow he would go to a phone store and ask if they could find out who it was registered to.

      Peter jumped when his own phone rang. He involuntarily synchronised his breathing with the ringtone, breathing in when the tune played, and out when it paused.

      An 0900 number. That could be the police.

      Just as he was about to answer it, the ringing stopped.

      Then it immediately rang again. He answered it this time.

      ‘Is this Mr De Haan?’ The voice sounded formal but friendly.

      ‘Yes.’

      ‘This is the Leiden constabulary of the Hollands Midden regional police. We’ve been looking for you, Mr De Haan.’

      ‘So I, er … so I understand. I …’ Peter felt his face redden. He would make a useless criminal, he thought. He would fall to pieces the minute he was interrogated.

      ‘Where are you at the moment? We can come and pick you up, if that’s easier for you.’

      ‘This is about Arnold van Tiegem, isn’t it? Is there any news?’

      ‘This will be easier if we discuss it face to face. I can send a car for you. That would be the quickest way, I think. Where are you now?’

      ‘I’m … I’ll come myself. I can walk.’

      ‘Sir, will you please—’

      Peter hung up. He put the telephones inside his jacket and stuffed his wallet into his trouser pocket.

      On his way outside he realised that his phone made him easy to trace. If he changed his mind and didn’t go to the police station after all, they would have no trouble finding him. He stopped at the faculty’s pigeonholes and slipped his own phone into the box that had his name above it. It was an intuitive decision that instantly felt right.

      He decided to visit Judith first. She was the only person he could talk to in confidence about this absurd situation, and her house was close to his route to the police station on the Langegracht.

      Less than ten minutes later, he arrived at the Sionshofje on a side street off the Haarlemmerstraat. He pushed open the heavy, green outer door and walked into the large inner courtyard, which was bordered by a brick pathway. There were no lights on in Mark’s house. He was away travelling of course, but Judith’s house was dark too. Surely it was too early for her to go to bed? Had she gone out?

      He looked through the window, but the living room looked deserted. He knew that Judith kept a key under a flower pot near the front door. He removed it, carefully opened the door and turned on the light.

      As he stepped through the door, a new message arrived.

      He opened it nervously.