Young Sherlock Holmes: Knife Edge (26 page)

‘I’m afraid your father was too clever for me,’ Sherlock admitted, ‘although I
am
on the verge of working out how it was done.’

‘Too late,’ Niamh said. She walked a little way off, but Sherlock didn’t turn to watch her.

‘Yes, too late,’ he agreed quietly, feeling sick at the thought that she blamed him, ‘but I still didn’t kill him. I wasn’t the one who
held the knife against his
throat and cut it open. I wasn’t the one who watched him bleed to death.’ His words were harsh, deliberately so, but she had hurt him with her accusation and he wanted to hurt her
back.

There was silence for a while. Sherlock thought that Niamh had left, but eventually she said: ‘I will always blame you.’

‘I know,’ he said, and then: ‘Niamh, did you know
about the tricks that your father was involved in? Did you know that the séances were faked?’ When she
didn’t answer, he added, ‘Did you help set up those threads to hang the material on, or was it you operating the light projector maybe?’

Still there was no reply. When he turned around, she had gone.

He walked towards the tower. He thought he knew now how the trick with the painting
had been done, but he had to make sure. Having a theory was no use unless you had the evidence to back it
up.

He started with the four lighter-coloured stones that stuck out of the base of the tower, the ones with iron rings set into them. Standing beside one of them, he did what he should have done
earlier, when he had first noticed them, and looked up the side of the tower. Yes! There,
about twenty feet up, was a dark space that had to be a hole in the stonework. It looked about the same
size as the holes at ground level that the stones were set in. About twenty more feet up, there was another hole. He walked around the circumference of the tower, noticing that there were
equivalent gaps above each of the four stones. They seemed to continue up to the top of the tower, every
twenty feet or so.

There was one more thing that he needed to know. Choosing one of the lighter stones at random, he walked directly away from the tower, keeping it at his back. He found that there was a faint
path through the underbrush where no bushes grew, and where the grass was stunted. Turning, he looked back at the lighter stone. If, he thought, a rope was attached to the iron ring
and a donkey or
a horse was attached to the rope then the stone could be pulled out of the tower. If all four of the stones were pulled out . . .

Now he had enough evidence, but if he wanted to persuade Mycroft and Amyus Crowe then he would have to build a scale model. Words wouldn’t be enough.

Before leaving for the castle, he went back to the tower and searched around the base. He
quickly found what he was looking for: fragments of the darker stone that the tower itself was made
from: the stone that was riddled with tiny air holes. They were surprisingly light in his hand, and he slipped them into his pocket for later.

Back at the castle, the police sergeant was interviewing servants in the reception room. He had obviously finished with the more important foreign
representatives. Sherlock noticed a bell on a
side table in the main hall. He rang it, and waited. After a few minutes Silman appeared. She looked, if anything, even more dour and vinegary than usual. The death of Sir Shadrach had obviously
shocked her.

‘Yes, sir?’ she said smoothly.

‘I need a large bowl of water and some sheets of card,’ he said. ‘Oh, and a jug of water as well. And
some scissors.’ He thought for a moment. ‘And four knives. And
some pins. Oh, and some sealing wax and a lit candle.’

She raised an eyebrow, but just said: ‘Yes, sir. Of course.’

‘And could you have them sent to the dining room for me?’

‘Given the circumstances, a cold collation has been set out in the dining room so that lunch can be taken whenever people wish. The table is nearly
full.’

‘Ah. All right – can you have the stuff brought to the library?’ It suddenly occurred to him that he hadn’t eaten lunch. ‘And can one of the servants put together a
plate of cold meat for me and bring it in?’

‘Yes, sir.’

In a fever of excitement, Sherlock went to the library to wait. While waiting he checked the shelves for books on geography and geology, and soon found what
he was looking for.

When the material and the food arrived he set to work. First he set the bowl on a table, and cut a circular cover for it out of card – its diameter a few inches larger than the diameter of
the bowl. In the centre of the cover he cut a hole. Next he made a long tube by rolling a sheet of the card up and fastening it with pins. He made a circular base for the tube, smaller
than the
cover on the bowl but wider than the tube itself, and fastened it to one end of the tube with some melted sealing wax.

Looking at it critically, he realized that he had to make some modifications to the tube. Using one of the knives he cut openings up the side to represent the windows in the folly, and then, to
finish it off, he made a series of small slices in the card of the
tube. He made them in groups of four, spaced equally around the circumference, and separated the groups of four along the length
of the tube by a few inches.

Now he was ready. Almost. He grabbed some food from the tray and stuffed it in his mouth, working while he chewed.

He slid the cardboard tube through the hole in the bowl cover, so that the circular base on the tube was pressed
against the underneath of the cover. The tube was slightly narrower than the
hole, so it slid easily back and forth. Then, because he didn’t want the underside of the tube’s base to get waterlogged, he melted some sealing wax and spread it over the base to seal
it.

Now to set the whole thing up. He put the card cover on the bowl of water so that the tube of card stuck up into the air,
and he let the tube drop down so that the circular base, the one he had
covered with sealing wax to waterproof it, was resting on the surface of the water. He then set the four knives out on top of the bowl’s cover around the circumference of the tube.

He stepped back to examine his handiwork, and realized with a curse that he had forgotten something. He needed to be able to get water into
the bowl. Grabbing one of the knives, he carefully cut
a square hole in the bowl’s cover.

Now
he was ready.

Without wanting to waste a precious second, he rushed out into the hall. As luck would have it, Mycroft and Amyus Crowe were standing by the door seeing the police sergeant out. They all shook
hands, and the policeman left. Mycroft turned and caught sight of Sherlock.

‘What
on earth is it?’ he asked. ‘You look like you used to do when you found a frog in the back garden and brought it into the house to show Mother.’

‘I know how the painting trick was done,’ he announced. ‘Come with me and I will demonstrate.’

Mycroft and Crowe followed him into the library. Mycroft took one look at the cardboard model on the table and said: ‘Of course! How could I have been
so blind?’

Crowe stared from him to Sherlock and back again. ‘Someone want to let me into the secret?’

Sherlock gestured to the model. ‘This is the folly – the tower out in the castle grounds.’

‘Right. I can see that.’

‘Did it seem to you that the tower is made of a rather unusual stone?’

‘Ah guess,’ Crowe admitted. ‘Quite porous, an’ quite dark.’

‘It’s actually called
“pumice stone”. It’s produced in volcanoes when the molten lava cools down.’ He took the flakes he had collected from his pocket and
handed them to Mycroft and to Amyus Crowe to examine.

‘Not many volcanoes in Ireland,’ Crowe noted.

‘Exactly. The stone was brought here from somewhere else. The key thing about pumice is that it has a lower density than water. Pumice stone
floats
on water.’

‘Ah think Ah see where you are goin’ with this.’

‘The tower is
made
out of pumice stone,’ Sherlock went on. ‘The pumice must have been shipped here from some volcanic location, carved into blocks and made into a
tower. The thing is that the tower doesn’t stop at the ground: it goes beneath the surface of the ground. I know that because I found its outer wall when I was investigating the
tunnels
beneath the castle. I thought it was just a blockage in the tunnel, but it was actually the tower itself.’

‘Down to where?’ Crowe asked.

‘Down to where the sea comes in through a series of caves. This whole area is riddled with caves. Somewhere at the base of the tower is a big block of pumice stone resting on the surface
of the sea – or at least, it does when the sea comes
in. When the sea is out then the pumice stone rests on the ground.’

‘And when the sea comes in,’ Crowe breathed, ‘the tower floats, and starts to rise.’

‘Exactly.’ Sherlock took the jug of water from the table and emptied it into the bowl through the hole that he had made. The increasing water level pushed the circular base of the
tower up, beneath the bowl’s cover, and the tower slowly
grew in height.

‘I couldn’t understand,’ he said, ‘why I could sometimes see the tower and sometimes couldn’t. At first I thought it was due to the landscape, but the real answer
is that it was sometimes taller and sometimes shorter.’

Crowe shook his head. ‘But we would have spotted the fact that the tower was growin’. We were there for hours, an’ it never changed.’

‘That was because
the anchors were in,’ Mycroft said. ‘Show him, Sherlock. I presume that is what the knives are for?’

Sherlock nodded. He had stopped pouring water into the bowl when four of the slits he had made in the cardboard folly had appeared above the level of the bowl cover. He put the jug down and slid
the knives across the card, one at a time, until they were all stuck in the tower’s wall, in the
slits. He picked up the jug again and poured more water into the bowl. The knives anchored the
tower in place. In the bowl, the water level crept up above the tower’s base, making the card wet, but Sherlock didn’t mind. He had made his point.

‘There are four large chunks of stone set around the tower,’ he said. ‘I wondered at first what they were, until I realized that they were
wedges
.
When the tower gets
to a certain height they can be hammered in to fix it in place. When the tower is meant to get smaller again, the wedges can be pulled out.’

Mycroft was frowning. ‘I presume that such an action could only occur at the time the water level is at a certain point, otherwise the tower might suddenly drop vertically through many
feet, and that could be catastrophic.’

‘I’m sure there’s a whole instruction book about how to raise and lower the tower,’ Sherlock said. ‘I’m still trying to work it all out.’

‘Ah presume this is somethin’ to do with smugglin’?’ Crowe asked. ‘Ah know that this part of the coastline was known for smugglin’, some years ago. The tower
would have given them a perfect place to hide their illegal goods. Put it in a room of the tower,
wait till the tide goes out, an’ then fix the tower in place so that the stuff is below the
ground. Ingenious!’

Sherlock pointed to the model. ‘And that explains the trick with the paintings. When we all looked out of the window of the room on top of the castle, the tower was at its lowest point
– below the line of bushes and trees. After we’d all trooped out of the castle, the wedges
were removed and the tower was allowed to rise up to its maximum height. I guess there was a
servant up there with a telescope, able to see into the room. They saw which painting I had hung up, and which way I had hung it, and then got a message to Ambrose Albano while he was staring away
from us and pretending to communicate with the dead.’

Crowe shook his head. ‘Such a complicated plan.’

‘Magic tricks are always complicated,’ Sherlock said. ‘I’ve learned that from Mr Albano. And they always use some kind of distraction. In this case, all the business with
the blue chalk dust was the distraction. It got us thinking about something completely different.’

Mycroft’s face took on a grim expression. ‘And Sir Shadrach’s death? How does that factor in to your explanation?’

‘I don’t know who killed him, or why,’ Sherlock said, ‘but I know how. The tower was allowed to sink to its lowest point, at low tide. The top of the tower is probably at
ground level then. Sir Shadrach was killed, and his bath chair was just wheeled on to the tower’s top. When the tide came back in, the tower rose up again, and the stone wedges were put in
place.’

‘There’s a flaw in your
argument,’ Crowe pointed out. ‘I doubt the sea level around here varies from low tide to high tide as much as the height of that tower. How do you
explain that?’

‘I think there are two things at work there. The first is that the sea is probably channelled through small tunnels and cracks, all the way into the cliff, and develops a much higher
pressure that way. That hydraulic pressure
is what pushes the tower up and down.’ He hesitated, thinking. ‘When Mycroft and I arrived, Sir Shadrach told us that the ascending room was
operated by hydraulic power, driven by the tides. The tower works in the same way, on a much more massive scale. The tower, when he discovered it, must have given him the idea for the ascending
room.’

‘And the second thing?’

‘I don’t think smugglers
would have wanted to be pinned to the rising and falling of the tides. I’m guessing that they had some kind of system of dams so they could pen up the
seawater and stop it getting to the base of the folly, or suddenly release that pent-up water and raise the folly whenever they wanted.’

Mycroft clapped his hands together. ‘Fascinating though this is – and it is fascinating, of that you should
have no doubt – it still brings us no closer to solving the mystery
of who killed Sir Shadrach.’

‘Do we
need
to solve it?’ Crowe’s face was serious. ‘The police are involved, and the auction will not take place. Our role here is finished.’

‘No,’ Sherlock said simply. ‘We can’t leave without finding the murderer.’