The real Chicago winter has finally reared its ugly head, and if you think the cold, slush and snow are tough on motorists, imagine what it’s like for the city’s bicycle messengers, those daredevils who risk life and limb in downtown traffic to make rush deliveries.

NIU sociology professor Jeffrey Kidder has a good idea.

Kidder, a former messenger himself, introduces readers to the profession and its fascinating subculture, exploring its appeal as well as its uncertainties and dangers, in his new book, “Urban Flow: Bike Messengers and the City.”