London 1916 and Great Britain is at war with Germany. Stylish lady detective Mss Isabel Hewitt is approached by a wealthy young woman Miss Jen-Eva Howard. She would like Miss Hewitt to look into the murder of her fiance, the journalist Giles Chichester. Isabel agrees, but soon discovers he was an unpleasant sort of man, who wrote contentious articles for his magazine and upset a lot of people. Convinced his death is connected with a case he was working on, Isabel goes undercover to follow up his leads, but the key to unlock the mystery is a white cat. The solution causes Isabel to question her hitherto unshakeable belief in justice."