Blind Search (Mercy Carr Mysteries, Bk. 2)

Especially for nine-year-old Henry, who's lost in the woods. Again. Only this time he sees something terrible. When a young woman is found shot through the heart with a fatal arrow, Mercy thinks that something is murder. But Henry, a math genius whose autism often silences him when he should speak up most, is not talking. Now there's a murderer hiding among the hunters in the forest--and Mercy and Elvis must team up with their crime-solving friends, game warden Troy Warner and search-and-rescue dog Susie Bear, to find the killer--before the killer finds Henry. 

When an early season blizzard hits the mountains, cutting them off from the rest of the world, the race is on to solve the crime, apprehend the murderer, and keep the boy safe until the snowplows get through.