My Grandparents' Christmas Mystery

You are playing as Michael whose Grandparents' (Mary and James) wanted to celebrate christmas alone without me and my parents this year. So instead we all agreed on meeting up the day after christmas, but after christmas was over my grandpa came to visit our home without grandma and looked in shock. We asked where grandma was but he just said she would come over later, 3 days passes and grandpa would never tell us what happened, all he said was to not go back to that cabin ever again. Then he passed away with heartfailure without telling us what actually happened and this left me with anger, confusion, sadness and a mission...to go find out what really happened that christmas and where grandma is...