Great way to start off the series.
It's about a girl, who goes in a mansion known as the Himuro Mansion to find her brother who has been missing after having gone there himself 2 weeks ago. While trying to find her missing brother she stumbles upon the mansion's wicked past of rituals and murders and such. The main antagonist is a girl called Kirie, who has something to do with the mansion being the way it is when Miku and her brother explore it.
The only two cons about this game is that Miku likes to randomly get stuck on everything and some shots you take don't count. But, other than that it's a really good game. I personally like the second one better though.