Chain of Criminality (Metaphor)
Holmes describes the criminal world and his relation to it as if it were a chain, each person representing a link. He identifies Porlock in particular as a weak link in that criminal chain: this weakness is what makes Porlock Holmes' ideal point of access to the chain as a whole.
Chemistry (Simile)
When Holmes hears about the murder of Douglas right after he has just deciphered the note alluding to this very thing, he is not particularly surprised. In fact, he shows practically no emotion. Instead, as Watson says, "his face showed rather the quiet and interested composure of the chemist who sees the crystals falling into position from his oversaturated solution" (171). This comparison to a scientist is an excellent because Holmes is generally emotionless, cerebral, meticulous, and quiet. His cases are like scientific experiments, his hypotheses similar to those of scientists.
Moriarty's misleading character (Simile)
MacDonald describes his meeting with Moriarty in the following way: "When he put his hand on my shoulder as we were parting, it was like a father's blessing before you go out into the cold, cruel world" (173). This simile expresses one of the most disconcerting aspects of Moriarty's character: the fact that he can be so apparently sagacious and warm. Clearly he is a master of legerdemain and manipulation; MacDonald knows this, but he cannot shake his positive impressions of the brilliant professor.
Holmes's brain as a tool (Metaphor)
Watson uses the metaphor of a tool to describe Holmes's brain. He says, "A long series of sterile weeks lay behind us, and here at last there was a fitting object for those remarkable powers which, like all special gifts, become irksome to their owner when they are not in use. That razor brain blunted and rusted with inaction" (178). When Holmes is not using his brain, it is rusty and dull; when he is using it, it comes alive and hums along with energy and power. The past weeks dulled Holmes's remarkable brain, and now it is kicking into high gear again. The rust is gone, and the edge is sharp once more.
The fly-like press (Simile)
White Mason states "We'll have the pressmen down like flies when they understand it" (189) when he tells MacDonald, Holmes, and Watson about the case. This simile works well because it implies just how fantastic and compelling this case is.
