Blood brothers / Nora Roberts.

Enhanced descriptions from Syndetics:

#1 New York Times bestselling author Nora Roberts presents the first novel in a compelling trilogy about three brothers bound by fate, blood, and a timeless enemy.

In the town of Hawkins Hollow, it's called The Seven. Every seven years, on the seventh day of the seventh month, strange things happen. It began when three young boys--Caleb, Fox, and Gage--went on a camping trip to The Pagan Stone...

It is only February, but Caleb Hawkins--descendant of the town founders--has already seen and felt the stirrings of evil. Though he can never forget the beginning of the terror in the woods twenty-one years ago, the signs have never been this strong before. Cal will need the help of his best friends Fox and Gage, but surprisingly he must rely on a stranger as well.

Reporter Quinn Black came to Hawkins Hollow hoping to make its eerie happenings the subject of her new book. She too can see the evil the locals cannot, somehow connecting her to the town--and to Cal. As winter turns to spring, they will shed their inhibitions, surrendering to a desire that will grow and form the cornerstone of a group of men and women bound by the fight against what is to come from out of the darkness...

Don't miss the other books in the Sign of Seven trilogy
The Hollow
The Pagan Stone