Murder in the Dark — Steve Demaree

Twelve people of diverse occupations and lifestyles receive an invitation to a free survivor weekend at a large remote inn. They are told to bring anything they might need to survive the weekend. The invitation promises them nice gifts, including an overnight stay in a castle. The winner of the weekend will receive even more lavish gifts. When they find out the gifts are legitimate, all of them plan to attend. Upon arriving, the butler informs them that they will be on their own for the rest of the weekend after he serves dinner. He will leave and the owner of the inn will stay in seclusion on the third floor. But during dinner on the first night, the lights go out, and one of the twelve guests is murdered. The others try to leave, but learn that all doors and windows are locked, so they must indeed survive the weekend until help comes.