Once upon a time, people knew who they were. Some were mechanics, some were politicians, some were writers.
Since about 1980, the real writers have been removed so that the rich tea party families could "write on the side".
That's why we had so many "situational tea party type Miss Marple comic murder mysteries", comic fantasies purely going with formula.
There is no "writing" here. It is formula stage play. It is a mixture of "Romancing the Stone", "Miss Marple", and virtually every stage comedy one has ever seen.
Then again, all good cinema begins as good stage plays, so you have at least a mediocre movie here.
What helps here is great casting. Margot Kidder is a bit like Lois Lane here, only more likable. She shows that comedy is her forte, and the role seems to have been written specifically for her.
This is probably what Kidder should always have done. The rest of the cast is also splendid.
In a formula film like this, casting makes a big difference. It's lightly likable, with the cast pulling it up over the 5/10 mark.