"And what did this… Russian Holmes want?" Lestrade asked.

"I can't claim to know, Inspector. He was gone before I could mount an investigation. Looking back, I have good reason to believe that I was not the first double he had encountered. For one, he hardly seemed fazed by the event and his quick departure was also quite telling. I cannot believe that any version of me would abandon such an extraordinary encounter unless he—I—already knew that engaging in conversation was a precarious choice." Holmes leaned forward, steepling his fingers. "Perhaps it is foolish of me then to chase another double… but I cannot abide an unsolved mystery."

"Holmes…" I cleared my throat. "This…"

"Appears impossible?"

"Yes!"

"Yet I have experienced it. You know me, Watson. I am a man of logic, but logic is only dictated by what men already understand. Tell me that swine fly and I will sneer your way… until I see them spreading their wings for myself. I have seen a version of myself and thus I will not sneer at Lestrade's assertion that he saw the same."

"Very well then, Holmes, but what does it mean? Scientists have theorized about other realities, other realms, but…"

"Let us find out then," Holmes said, just as our cab pulled up beside a large, stone building.