"Holmes!" I cried. The water was dark and I could not make out the person who was now well beneath the surface. The water rippled around the point he had jumped in, and all I could see was my own reflection, and that of the boy.

"Why did you let him jump in?" I asked, angrily.
"I didn't know he was going to jump in, Sir! He says a shilling if he can borrow this old anchor is all, and would I mind holding his coat and that!"

My mind raced; I was sure Holmes had a sound scientific reason for throwing himself into the Serpentine in the dead of winter, but surely this was suicide. I am no swimmer, and in any case would be unable to locate my friend in the lake.

"Holmes! Good God!" I cried and sunk my hands below the surface as if to reach for him. "Get help, boy!" I shouted at the young man.
"Who from, Sir?" he asked, now as panicked as was I.

I glared at him; I did not know the area well. "Find a Constable!"

He ran off.

I yearned to jump in after him but my head won rule over my heart and I remained on the pier. My cries of my friend's name faded to a mere whisper as the minutes went on. By the time the youth returned with not one, but two Constables, I was sitting on the edge of the pier staring into the water.

"How long has he been down there, Sir?"

"Five or six minutes," I replied, sadly. I stared as the wind whipped at the surface.

"We'll not find him now, Sir."

"Suicide," said the other officer.
I wanted to correct him but could find neither words nor reason. But I was about to receive my second serious shock of the hour.

Six feet from the end of the pier, a black box suddenly popped, cork-like, to the surface. Following it was a flurry of water, and the flapping of cloth.

"Holmes!" I cried. The two Constables, as surprised as I, helped me drag Holmes out by the shoulders. He was ashen, with a blue tinge to the lips and eyelids, and could only speak in a whisper.

I realised part of his plan, and took the blanket from the edge where the boy had placed it on Holmes' coat. I wrapped him in it.
"Watson-" he began.
We tried to pull him to his feet but he could not stand on his own. I threw his coat around him atop the blanket and I held him up with one of the policemen. We made to walk him back to Lancaster gate. I reached for my brandy flask.

"Wait!" whispered Holmes. He reached into his sodden waistcoat pocket and produced a crown. He handed it to the boy.

"I am afraid I lost your anchor."

The boy stood stunned as we led Holmes away. We hailed a Hansom.

The cabbie was dismayed at Holmes wet state. The journey was a short one, and for it I paid six shillings.

I almost had to carry him up the stairs at our rooms.

"Gracious!" cried Mrs Hudson on seeing the frigid Holmes. "Whatever is the matter?"
"Mr Holmes decided to go for a swim," I said, angry and concerned.

"Good Lord!"

"Would you kindly stoke up the fire and fill some hot water bottles? He is suffering somewhat from hypothermia."

Mrs Hudson did as she was asked, going to fetch wood and bottles. As I got him to the stop of the stairs, we both fell in through the door. Holmes lay with his eyes closed and his breathing shallow. I groaned as I felt the warm stab in my leg return. I dragged the chaise closer to the fire and laid Holmes upon it. Placing all delicacies aside, I had to remove his clothes. It is extremely difficult to undress a wet, semi-conscious man.

When my task was complete I wrapped him in blankets and put my flask to his lips. He rallied a little and the blue tinge faded from his face. His eyes opened.

"What in the devil's name were you thinking, Holmes?" I exclaimed.

He muttered and I slapped his face. "Wake up!"

Mrs Hudson entered with the hot water bottles and I placed them about the bundle. The wood added to the fire burned with a more fierce flame and it was soon very hot close to it. Holmes colour began to return. I checked his pulse and watched him keenly for almost an hour. Finally, he regained enough composure to speak once more.

I was stricken with both relief and rage. "Why, Holmes?"
"Thank you, Watson. Without you I do not think I should have made it to safety."

"You almost left me behind, both here and at the water!"
"I was afraid you might try and stop me."
"Indeed I would have if I had known for an instant what you meant to do!"
"I feared as much." Holmes coughed his sentence out. I fed him a little more brandy.

"Did you inhale water?" I asked.

"No. There was a great pressure on my chest."
"How deep did you go?"
"To the bottom."

I was surprised. The Serpentine is not deep, but it is certainly deep enough to cause great discomfort.

"I needed to perform a vital experiment."
"On yourself?"
"On the box."

"The box?"
"You recall the glowing orbs we saw at Cheapside?"
"Indeed."

"The material we found was part of a sphere with a hole in."
"Yes."
"It is a helmet of sorts. It is possible to go into the water, and when weighed down, sink all the way to the bottom. Enough air can be held in a pocket in the helmet to allow the wearer to breathe for some minutes. I imagine it is more useful in the summer months. The cold water made it extremely difficult to breathe in and out."
"I see." My ire gave way more to sympathy and intrigue.

"The box made the atmosphere quite dark, but a transparent orb would give a much better view, if only of a foot or so. It might even be possible to contain a light within, though that would make the reflection bothersome. On letting go of the weight, one does pop rightly to the surface. This is most useful, for after a few minutes the air inside the box becomes thin and sour."

"The glowing orbs were helmets?"

"Indeed. It was difficult at lower depths to keep hold of the box, as the water tried to snatch it back to the surface. If I had let it go, it should have come quite violently to the surface. Given sufficient depths as in the river, surely the orb would crush. The box became quite bent, and though the dome is a stronger shape, it too would have a pressure beyond which it could not remain intact. If indeed a light were contained inside as we saw, it might melt the material. Once melted even a little, it would become extremely flammable and explosive."

I realised that what we hade seen may well have been the departure of these helmets form the heads of small boys whilst they were underwater.

"The shards in the boy's face probably came from an imploding or exploding orb," I said.

"Indeed," said Holmes. "We must go to Bermondsey at once!"
"You are not going anywhere for now, Holmes. You shall be lucky not to catch the pneumonia. I shall send for Lestrade."