Plot Summary:When Maria Gibson is shot through the head while standing on the Thor Bridge on her estate, the family's governess, Grace Dunbar, is arrested for murder. Not only does she admit meeting her mistress on the bridge, the police find the murder weapon in her room. She vehemently denies killing the woman and Senator J. Neil Gibson, the dead woman's husband, believes her. He hires Sherlock Holmes to get to the bottom of it all. The Senator admits that he and Miss Dunbar have affections for one another but that neither of them had anything to do with the murder. Dr. Watson is convinced that the Senator is the culprit but Holmes comes to an entirely different conclusion.