Outwitted sharpers. A rook is a sharper, and a rookery the place of resort for sharpers. A rook is the opposite of a pigeon; a rook cheats, a pigeon is the one cheated.
“This light, young, gay in appearance, the thoughtless
youth of wit and pleasure - the pigeon rather than the rook - but the
heart the same sly, shrewd, cold-blooded calculator.”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894