Ah shit, just started this anime and I'm already at episode 5, I like it so far the mysteries and case solving is going pretty good. This is like Toradora but without school life and more adventure, killing, and case solving. This is like a baby of Toradora and Psycho-Pass to put it in a way.
That OP man.
Here's the plot:
Gosick takes place in 1924 in a small, French-speaking fictional European country, which stretches in a strip from Switzerland, through the alps between France and Italy, to the Mediterranean Sea. The country is called "Sauville" in the English translation of the light novels; it is called "Saubure" in the anime adaption. The story centers on Kazuya Kujo, the third son of a high-ranking officer of Japanese Imperial Army, who is a transfer student to St. Marguerite Academy, where urban legends and horror stories are all the rage. There he meets Victorique, a mysterious yet beautiful and brilliant girl who never comes to class and spends her days reading the entire content of the library or solving mysteries that even detectives can't solve. The series mostly focuses on Kazuya and Victorique getting involved in different mystery cases and their struggle to solve them, at the same time forming important bonds with different people.
The anime/manga is old itself looking at the wiki it's original run was from December 10, 2003 - July 23, 2011.
I would suggest it to people who liked psycho pass, detective conan, etc.