The story is Dahl's variation on a popular anecdote dating back at least to 1939:[1] a married woman receives a glamorous mink coat from a man with whom she had an affair.
Once a month, Mrs Bixby travels from New York City to Baltimore, supposedly visiting her elderly aunt; in fact, she is having an affair with the Colonel.
As she is preparing to leave after one of these visits to Baltimore, Mrs Bixby receives a package from the Colonel containing a letter and an expensive gift: a dark mink coat.
The Colonel's letter informs Mrs Bixby they can no longer see each other, and suggests she tell her husband the mink coat is a Christmas present from her aunt.
But as she leaves her husband's office, Dr Bixby's secretary, Miss Pulteney, walks proudly past her, wearing the mink coat.