Welcome to Baker Street

67. How to get away with murder

"There was never a witness, Holmes," Anderson corrects him.

"And yet you listened to Isaac's interrogation," he fulminates against him. "That boy has had troubles sleeping since he was a child, and I'm willing to bet that he was awake that night, too. To be precise, we know he was up, for he saw a man coming out of the woods—you all heard his words. He simply absorbed that memory into his dreams and always thought that he had only dreamed of it."

"Wait, Sherlock, I perfectly remember that Isaac claimed that he never saw the phantom's face. Even assuming that he wasn't dreaming and imagining it all, how can you say with certainty that it was Fred Admiral?" Lestrade asks him doubtfully. He has the impression that Sherlock is building castles in the air.

"Because the boy affirmed that the man he saw was wearing a grey coverall. It's pretty obvious now, isn't it?"

Everybody looks at him with wide eyes and confused expressions on their faces. The detective stares into their vacant looks and sighs heavily.

"Do you ever hear an echo in the deserted void that is in your minds?"

He fishes his phone out of his pocket and makes a call. When someone picks up, he quickly states, "Hello, Sergeant Donovan. I need to speak to Isaac. Put him through, please."

He puts it on speaker, and everyone can hear Donovan hissing, "I'm not your assistant," before a male voice replaces hers.

"Hello?"

"Hi Isaac, this is Sherlock Holmes. I just need to ask you a few things. I noticed that you're quite an observant person: do you remember what I was wearing when I interrogated you this morning?" He inquires, earning disconcerted looks by all present. Where is he getting at?

"Yes," is the laconic answer coming from the other end of the line.

"Do you recall my shirt?" Holms tries to get something more out of him.

"I do." Another curt reply. Isaac isn't exactly a chatterbox.

Five pairs of ears are listening to the conversation, but only one person knows where this is going.

"What colour was it?" Sherlock encourages him.

"Lilac. It was a lilac shirt," Isaac affirms confidently.

Everyone frowns at that statement as they are all staring at the light blue shirt that Sherlock has on: it's the same one he was wearing at New Scotland Yard a few hours before.

"Are you sure, Isaac?" He questions, faking a distrustful tone for the benefit of his sceptical audience.

"Yes, I am. Truth be told, I found it weird, but I have no taste in fashion, so I can't be the judge of that," the boy replies tersely. At least no one can doubt his bluntness.

"Thank you. That'd be all," and with that, Sherlock ends the call.

"What does it mean?" Anderson asks, puzzled.

Sherlock patronises him. "It means that you don't pay attention to details. When we went to Isaac's room, you questioned his football faith while looking at the Arsenal crest coloured in green and lilac. What you didn't realise, though, is that Isaac isn't an inattentive fan; he is colourblind. Deuteranope, to be exact. People with deuteranopia are likely to confuse mid-reds with mid-greens, or light blues with lilac (as was the case both for the Arsenal drawing and my shirt). But they can also confuse blue with grey, so the man with a grey coverall that he saw coming out of the woods was actually wearing blue clothes. And I think we all know what a plumber's uniform looks like," he concludes, gesturing towards the entrance of the house, where Fred Admiral has just appeared on the threshold, wearing a blue coverall.