Murder Myster in the Making

My wife is a huge murder mystery fan. Not just ANY murder mystery though. None of this blood and guts murder mystery. That type of murder mystery is so depressing--and usually predictable. No, she prefers a murder mystery that you could picture Dick Van Dyke, Angela Landsbury, or Buddy Ebsen starring in. A murder mystery with some humor. Can you dig it? So, she's enlisting my humble assistance to come up with a plot for this yet unnamed mystery. Also, could I please come up with a catchy title; and, oh yeah, some good characters, and a good story line too. She promises to give me credit in the book's intro. One more thing, she wants to make lots of money on this book too. So, if you have any ideas, feel free to forward them to us. This'll be great. Really...