When a busload of passengers is stranded by a blizzard in upstate New York, they find their way to an old mansion in the woods, now St. Mary's Convent, where the Reverend Mother Mary Cecilia provides them lodging for the night. Unfortunately, she soon realizes that among her guests is likely to be a serial killer known as "the Mary Murderer" whose victims are all named Mary! Though most of the sisters have been stranded in Buffalo, the four nuns remaining with her all have the first name Mary, as do two of the women on the bus. To add to the list of potential victims, one passenger is a flamboyant actress whose TV character is named Mary and another is a retired school teacher who was formerly... you guessed it! ... a nun named Mary! Before the night is over, the killer strikes! Which person from the bus could be the Mary Murderer? The college professor? The newspaper columnist? The bus driver? Luckily, police detective Patrick McDougal was also on the bus and takes charge of solving the case. Providing as many laughs as chills, Murder Can Be Habit-Forming is a light-hearted mystery comedy that reveals the very human side of the nuns as they attempt to stay one step ahead of the killer.