The following story is with thanks to Ballykissangel, who provided me with this prompt: "John can't swim but Sherlock doesn't know it."
Word Count: 509 words.
I watched in horror as Holmes threw aside his hat, coat, gloves and cane before diving into the Thames after our retreating criminal and his sack full of silver.
"The goods will weigh him down, Watson! Quickly! Your assistance!" he barked at me as he took to the water.
I shivered and paced the bank fearfully, feeling perfectly helpless. My old war wounds have left me quite unable to swim in such tepid water. Indeed, it is rather difficult for me to swim even in warmer waters.
"Watson!" my companion called to me desperately.
I considered taking to the water to assist him, but knew that doing so would only provide him with more to concern himself with. "I am sorry Holmes," I called back. Of course I was sorry; sorry to be so utterly useless to him at a time like this and sorry to have not thought to inform him that I was unable to swim.
I stopped my anxious pacing and turned my attention to the surface of the river. Both the thief and Holmes had vanished from view. I stood there trembling. What could I do?
After what felt like an age, I saw my companion's head break the surface of the water. He coughed loudly and started back for the bank upon which I stood, dragging the still form of the man that we had pursued across London with him.
"The silver is at the bottom of the damned river!" Holmes informed me angrily as I assisted him in removing the criminal from the water. I could see that he was shaking violently and wondered whether it was with cold or rage.
I offered my companion my hand and repeated my apology.
He glared at me resentfully and attempted to escape the Thames without my assistance. "Why did you not help me when I asked?" he demanded.
I shook my head and crouched before him, ignoring the protests of my injured leg as I did so. "I cannot swim," I confessed quietly.
His expression immediately became one of disbelief. "Not at all?"
I averted my gaze and shook my head.
"Then you must learn!" my companion remarked as he at last grasped my hand.
I almost released my grip at his words in fear that he was about to pull me in. "I did learn; I simply am no longer able to do so."
Comprehension dawned and he nodded as I assisted him in dragging himself onto the bank. "Your wounds."
"Quite so," I confirmed as I draped his coat about his quaking shoulders.
He lightly touched my shoulder before turning his attention to our criminal.
I am glad to report that Holmes had managed to haul the thief to the surface of the river before he drowned and that Scotland Yard were able to retrieve the stolen silverware.
Never again have I neglected to inform Holmes of one of my inabilities and, for his part, my companion does try to avoid taking my assistance for granted. Every man has his limitations, after all.