Hyouka

Synopsis

At the request of his older sister, Houtarou Oreki joins his high school's Classic Literature Club to stop it from being abolished. He meets Eru Chitanda in the club room, and after a short conversation he wonders why she was able to enter the room without a key, which he obtained earlier. They are interrupted by Satoshi Fukube, and as Houtarou tries to leave he is stopped by Eru who wants to know how the room was locked in. He then explains that the cleaner was there to lock the room with spare keys, thus hinting at an aptitude for logical deduction. The next day he tricks Eru into focusing on a made-up mystery to prevent her from dragging him to the distant Music Room and wasting his energy solving another mystery. On his way home with Satoshi, he gives an explanation for the avoided Music Room incident. 

(Source: Wikipedia)