Shrewd

Clever at understanding.
Showing a good judgement  to solve a situation.

Characterized by sharp intelligence and often a sense of the practical.
Sagacious, astute, perspicacious.

A shrewd observation by Sherlock Holmes: "It’s a wicked world, and when a clever man turns his brains to crime it is the worst of all."  Sherlock Holmes in “The Adventure of the Speckled Band”


Source: http://andynaselli.com/a-shrewd-observation-by-sherlock-holmes