Tomorrow at Ten (1963)

A surprisingly engaging feature sees John Gregson as a detective ("Insp. Parnell") brought into investigate the kidnap of the son of the wealthy "Chester" (Alec Clunes). Interestingly the kidnapper "Marlow" (Robert Shaw) has locked the child into an attic room in an unknown London address then gone to the man's home to demand the ransom in person - so we know all the characters from the start. Midway through, he there is an altercation and suffice to say the policeman has to try and track down the child from scratch. It's quite suspenseful, and the tight-knit cast keep the story moving well with quite a degree of jeopardy building, too.