Shadow of a Doubt.

Sit Muk-fu covets the beauty of the maidservant Ku Kar-lin. Ku concocts a scheme with her husband Wong Hoi to swindle money out of the lascivious man and has to flee into hiding with Sit being stabbed to death during their secret liaison. Detector Lui Hak investigates into the murder at Ku's house and arrests the husband who has a sharp knife in his possession. Bearing witness to the murder, their daughter Bo-bo fights to prove her father's innocence. Upon receiving a score of mysterious phone calls revealing Ku's whereabouts, Lui lures the woman out with Bo-bo as bait, subduing and detaining the suspect. The detective fathoms the mystery of the murder case which leads him to another suspect, But Kei. But has been extorting money from Sit and forces his daughter, the sole heir to his inheritance, into marriage in return for concealing his murder-for-money scheme. But submits to arrest without resistance while Ku and husband walk free, acquitted of the charges.