Marie Morgan's 21st birthday is also the 13th anniversary of the day her grandfather told the Morgan family about his will. Marie has instructions to open and read the will in her grandfather's house, at a table set for 13 guests. When Marie opens the envelope containing the will, someone tries to murder her. Adams Morgan hires private detective Johnny Smith to solve the attempted murder. Before the mystery can be solved, three other members of the Morgan family are killed. And as Johnny tries to find the murderer, he falls in love with Marie.