Manga de Wakaru Angou

Inspector Jun Meguro has been tasked with tracking down a crafty art thief who leaves clues in the form of perplexing cryptographic puzzles. Lucky for him, his sister Ruko is a math whiz who is willing to teach him about cryptography so that he can crack the case. But can they decode the thief’s ciphers before she steals again?

(Source: No Starch Press)