It was cold, bitterly cold, in the grey, institutional room. The smell of stale smoke, testosterone and body odour was overpowering. The striplighting overhead cast a chilly, clinical light on the room, making it seem even more depressing. Plus one of the lights was on the blink, and kept flashing on and off, while simultaneously making an annoying buzzing sound that was doing his head in.

But Sherlock, as murderous cabbies-cum-serial-killers were so wont to point out, would do anything, anything at all, not to be bored. That's why he now found himself in the visitors' room at HM Prison Pentonville, sitting on a plastic chair which was bolted to the floor, desperately trying to squeeze some entertainment value out of the middle-aged man in front of him, just the other side of the shabby formica table.

The man had written to him, begging for help in clearing his name, insisting he was innocent of the murder charge on which he'd been convicted. At first glance, it had seemed promising. But sitting here now, face to face with the prisoner, Sherlock was becoming increasingly convinced that he was dealing with a straightforward, bog-standard, straight-from-central-casting domestic. The man had gone to jail, he had gone straight to jail, and, as far as Sherlock could see, he would not be passing 'Go' or collecting £200 any time soon. Dull!

He flicked through the file on the table in front of him.

"Oh dear," he observed, languidly. "Your lover appears to have been the victim of a particularly brutal murder, shortly after the two of you returned from an evening's drinking at your local watering hole, The Horse and Trifle."

The prisoner wiped a tear from his eye. "It was brutal. Somebody wasn't taking any chances. Smothered with a pillow, beaten about the head with a blunt object and stabbed through the heart with a kitchen knife, I found his body lying at the foot of the stairs when I got up the next morning."

"Dangling participles!" murmured Sherlock.

"What?" asked the prisoner, startled.

"The participles don't agree with the subject of the sentence. At least, I assume they don't. If I'm mistaken, then I really ought to congratulate you on a quite miraculous recovery."

The prisoner looked at him blankly.

Sherlock stared back, a sardonic smile playing on his lips. "And you didn't hear anything, while all this smothering, beating and stabbing was going on?"

"I'm a very sound sleeper. A bomb could have gone off in the next room and I wouldn't of heard it."

"Wouldn't have!"

"Sorry," blushed the prisoner. "I always was a bit sloppy with my pronounciation."

"Pronunciation!"

Sherlock cleared his throat, consulted his notes again, and then continued, "Several people who were drinking at the Horse and Trifle that evening distinctly recalled that the two of you had a violent argument while you were there. Five separate witnesses remember you shouting, 'Just you wait, I'll kill you!' at the deceased, not long before the two of you left."

The prisoner shifted in his seat. "It was just a figure of speech. I didn't mean it! I'll bet you that thousands of Londoners threaten to kill someone every year. Less than 200 actually do."

"Fewer than 200!" snarled Sherlock. "You're only supposed to use 'less' with uncountable nouns!"

"You've got to believe me, Mr Holmes! That kind of talk was just lighthearted banter. It was typical of Peter and I…"

"It was typical of Peter and me, actually…"

The prisoner looked shocked. "You had something going on with Peter, as well? The twelve-timing tart! If he were here now, I'd kill him again!"

"No, no, you misunderstand me," explained Sherlock, hurriedly. "I never even met Peter. And, anyway, I'm an asexual, not-my-area, the-rest-is-transport sort of thingy. The point I was trying to make is that it should be 'me', not 'I', if you're using the pronoun in the objective case, no matter if it's a singular or plural object….Hang on a minute, what do you mean, 'kill him again'? I take it that that was a confession?"

"No, it bloody wasn't! I didn't do it!"

"But a jury found you guilty, did they not?"

"I didn't get a fair trial, Mr Holmes! The jury weren't even listening to the evidence. Some of them had brought in crosswords and Play Stations and I could see it on their faces that they were disinterested."

"Uninterested, " Sherlock muttered, a mixture of irritation and ennui etched on his face. "A jury's supposed to be disinterested – that's kind of the point."

He sighed, got up from his seat and carefully fitted his leather gloves to his long, slender fingers.

"This has been a complete waste of my time. I don't really know what the point of this conversation has been. In fact, at times I have had the distinct impression that this entire dialogue has been constructed solely so that some grammar Nazi can insert as many of his linguistic pet peeves as humanly possible and prove what a superior smartypants he is. There is nothing I can do for you. If you have any complaints about the conduct of the trial, I suggest you consult a lawyer."

The prisoner was clearly crushed by Sherlock's refusal to help, but he tried to put a brave face on it.

"Ah, well," he shrugged, "at least I tried. I suppose it could be worse. It's a good job I'm not in Belarus. If I were, I could be hanged for this!"

Sherlock snorted, contemptuously. "No, you couldn't. You could be shot. Do your research!"