On the French Riviera, a reclusive oil millionaire bequeaths his fortune to the survivor among his potential beneficiaries. These are his granddaughters [nieces?], secretary, and attorney. Fearing for his life, the lawyer hires a private investigator. The attorney, secretary, and nurse are subsequently murdered. Rescuing one granddaughter from the magnate's assistant, the detective learns that the assassin has been hired to slay all heirs save the other granddaughter. After the millionaire dies of a heart attack, the heiress is arrested, and the fortune passes to her innocent sister. Intent on donating the money to charity, the granddaughter leaves with the detective.