After receiving a letter whose contents leave him highly distressed, Colonel Stenhurst reaches out to hire private investigator Slim Calaghan to watch his step-daughter, Viola Alardyse. But before Calaghan can meet his prospective client and get on the case, he is intercepted by Viola herself, who suggests that he not carry out the Colonel's wishes under threat of police involvement. And Calaghan learns that the Colonel has been shot mere minutes before their arranged meeting, he knows something sinister is afoot and vows to find the person-or persons-responsible for the foul deed.