If the death of Doctor Watson had been of natural causes, his widow Mrs. Mary N. Watson would have grieved the loss of her husband for a time then moved on with her life. However on re-discovering his certificate of death she is again is faced with the troubling fact that the cause of his passing had been recorded as being of an indeterminate origin. With this Mary Watson again takes up the role of consulting detective and sets to find out 'who and why'.