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Imagine Eric's delight when, one day, a little man with a propeller on his back appears hovering at the window! It's Karlson and he lives in a house on the roof. Soon Eric and Karlson are sharing all sorts of adventures, from tackling thieves and playing tricks to looping the loop and running across the rooftops. Fun …

Bill Bergson, Master Detective is a children's novel by Astrid Lindgren. It is the first in the series about the Swedish boy detective Bill Bergson.