A film made for the Metropolitan police warning against careless actions leading to crime.
A shop window is smashed and a hand grabs pearl necklaces and other items, a man runs to a car and is driven away. A small flag? is stuck into an enormous map, a plain clothed policeman walks past other wall high maps of London. WS of radio control room, uniformed police speak into microphones.
A suited man is seen walking in a quiet suburban street, he knocks on a front door and notices full milk bottles, newspaper still in letter box, and an open window. He pretends to walk away but returns. Underneath the door mat he finds the house key and enters. A lady neighbour notices him and dials 999. Unaware the man leaves the house but moments later he is picked up by the police.
A series of thoughtless acts are shown to illustrate opportunistic crimes. A young women brushes her hair in a public toilet and leaves her gold wrist watch and ring behind. A secretary finishes typing a letter and leaves her handbag on her desk open showing money. A business man is escorted from a waiting room, he leaves his brief case behind. Two business men are talking in a pub, near them a third man listens to their conversation. He is then seen sitting in his car as one of the business men leaves a bank with a brief case. He snatches the bag. Newspaper accounts of robbery. A middle-aged lady drives and parks her Rover car near to a shopping centre, she leaves the car unlocked. A respectably dressed young man goes over to the car sees the keys in the ignition and a radio and binocular on the seat. He drives the car away and steals the items.
Back at police H.Q. more Markers are stuck into the wall maps. The film ends with the warning "STOP! A LITTLE FORETHOUGHT CAN REDUCE LONDON'S CRIME'.