The Murder-of-the-Month Club: Murder Is a Charade, Until...

Six senior citizen residents of an old inn in a village on the Channel Coast in England form a club to do in six other seniors whose factory smoke creates a killer smog. They merely plan a charade of murder, one a month from spring to autumn. But those on their list do die, and in the order and by the method they choose. Who is actually doing in those on their list?