‘Come with me now, Mr Buttons. I will make sure that you are treated fairly,’ said my friend, now only ten feet from the boy. He reached out his hand towards Buttons.

A wind had come up and the trees nearby moaned with the sudden gusts.

‘No! Get back! I am a sinner! I have sinned! Only God can forgive me!’ cried Buttons as he recoiled from Holmes’s outstretched hand and backed further towards the centre of the bridge.

A bolt of lightning bleached the sky and a crack of thunder sounded milliseconds later. And before we could stop him, Buttons catapulted over the railing, plunging into the black waters of the Jesus Lock.

We both ran to the edge. There was no trace of him. Only dull concentric ripples where his body had entered the water, broken by raindrops distorting the widening rings.

‘Get help, Watson!’ cried Holmes, tearing off his coat.

PART EIGHT

THE UNLOCKING

‘Let him have the key of thy heart, who hath the lock of his own.’

—Sir Thomas Browne

CHAPTER 38

Rescue

‘My God!’ I cried. ‘Can he swim?’ I struggled to remove my boots.

‘Watson, no! Your leg!’ shouted Holmes. ‘Get help!’

He plunged into the water.

I stood frozen as I witnessed the boy surface with a strangled cry some distance away, then go under, and surface again. His arms flailed, he gasped for air. ‘Help!’ he cried and went under again. Holmes swam with strong strokes towards the drowning boy. But the boy’s survival instinct and panic would endanger anyone trying to save him.

I could not leave them. I looked about for a pole, for a rope – something to toss to Holmes.

Lightning flashed again across the sky. It was five in the morning. Would anyone be near? It was then that I heard bells and a police whistle. I turned to see a police van pulled by four horses, lanterns blazing, racing towards us from some distance away down Chesterton Road.

Then I remembered that Holmes had asked the young officer with Polly to send men to the rectory! Limping from the bridge into the centre of the road, I waved my arms to stop them.

Turning back, I saw that Holmes and the boy had disappeared. The water near where the boy had surfaced was roiling and a pair of white hands emerged and then went under.

And then, on the other side of the river, I saw something that made me freeze in terror. A figure swathed in a dark, shapeless coat and hood ran across the lock gates to the lock controls, seizing the crank handle and opening the sluice gates.

Lightning flashed and the top half of the face was revealed, eyes fierce and mad, but the lower half of the face was covered by a heavy scarf, even in this steamy, hot night.