Detroit private investigator Jonathan Raines, an ex-Marine and war veteran, is hired by Hudson Motor Co. executive Willis Ponder to shadow beautiful Eunice Ponder and chronicle her romantic adventures. Surprisingly, Eunice Ponder finds him instead, offering him a sizeable sum of money to follow her, too!
While unconventional, he accepts both proposals and follows her to the opulent new Book Cadillac Hotel where she entices him to stay with her in an empty penthouse apartment on the thirty-second floor. With great internal conflict, Raines declines the invitation, discovers the identity of the man who leases the penthouse, and reports his findings to Willis Ponder.
The next day, he is told Eunice Ponder has been killed while asleep in the penthouse. Although his job may be over, Raines now wants to find out who killed Eunice Ponder. He returns to the penthouse to find Eunice’s sister, Christine Dehavilland, who is searching for Eunice’s notebook which may contain clues as to why she was killed.
Raines learns that Eunice is not Willis Ponder’s wife, as he had believed, but his daughter-in-law, married to William Ponder, also an executive at Hudson. Later, while at a popular speakeasy west of Detroit, a carload of gunmen opens fire on Raines as he emerges from the club, wounding him and killing a woman nearby. Two of the gunmen are shot dead dead but one gets away.
Now Raines must find who is trying to have him killed and is helped by Bernadette Robbins, a Detroit Free Press reporter, and George Matrikos, a shady police detective.
Raines discovers penthouse owner Nathaniel Sarrow, a gem dealer who actually is the notorious Midwest hit man known as The Jeweler. Through a series of encounters, Raines and Bernie Robbins find Sarrow in a warehouse where they are captured and are to be executed when Matrikos intervenes to save them.
The trail of suspects includes Henry Ford’s son, Edsel, who now is president of Ford Motor Co., and Harry Bennett, the elder Ford’s henchman who does a lot of the dirty work. Others who pop up are a couple of operatives for Bennett, and a Chicago gunman connected to Al Capone. Both Ponders and Christine Dehavilland also are on the list.
Raines gathers the suspects inside Detroit’s famed Graystone Ballroom. As Raines weeds through the potential killers, eliminating them one-by-one, it appears clear that the killer is Christine Dehavilland, who is named in the notebook as being involved in industrial espionage between Hudson and Ford. Christine has been selling manufacturing secrets to Bennett at Ford and Eunice was about to expose the criminal activity.
However, Christine has a gun and uses Bernie as a human shield, escaping to Windsor, Ontario, where Raines follows. That night he finds Christine murdered and tracks down her killer on a passenger train outside of Sarnia, Ontario.