It was about two teenage boys who goes missing in the mountains while hiking. They are pressumed dead, but the girlfriend of the missing boy, who is also the sister of the other guy will not give up after finding unexplanable things in her brother's room. With the help of her boyfriend's brother they go searching for answers. Meanwhile another story plot is opened when they introduce two brothers who some how holds the answers that they are looking for.

I've must have read the book in the 80's and I would love to reread it. Help!