What's the Name of That Book??? discussion

The story starts out with a detective and he's partner walking into the store of a gas station (or car wash maybe) and some crazy druggie walks in shoots the place up, kills the partner of the detective (can't remember any names). The detective survives the attack and kills the guy. After the traumatic experiance the detective decides to move himself and his family away. It turns out his old partner, who has long lived on a nice property in Montana has recently past away, and left the estate to the detective. So he and his family move there. Turns out there is a dark entity there, that seems to be learning to controll anymals, none of which survive the mindcontroll for long. The family starts getting weird dreams. They understand the entity is trying to get into their heads, asking them to open the door or let it in. They win in the end, because the son finds a way to trap the entity in his own mind, somehow, I'm sorry, I forget the details. And I could be wrong about some minor things, but this is the jist of it, and I can't find this anywhere! It could be Steven King, but I think I would remember that, so I'll just say that I dont know who the author is. This was a really good one, and I'm very sad that I can't recomend it to anyone, because I have no idea what it was called or who the author was. Thanks in advance to anyone who even wants to help! :)

Could it be Winter Moon by Dean Koontz?

Thank you so much. Solved! im sorry for not checking in sooner, but here I am in time to get this as a gift for halloween.

Glad you found your book, Dāvis. Thanks for the update.