Policemen are seen on the beat, on point duty, in a car, in a motor launch and on horseback. A news placard announces the declaration of war. Members of the war reserve police are measured and fitted for uniforms before marching out for the first time.

At Peel House, a class is held in the Constables Training School, where an accident is simulated, a mock trial is held, traffic control is demonstrated with model streets and vehicles, and there is a gas drill. Meanwhile, the regular police officers practice decontamination and firefighting. Volunteers attend a judo class.

Holland and Belgium are invaded. Men in a café listen to a broadcast about the formation of the Local Defence Volunteers (Home Guard) and queue to volunteer. Police check their credentials. Italian men are taken from their businesses. The French government surrenders. At a police station, a desk sergeant gives advice to members of the public. A driver and two hikers have their identity papers checked.

When an air raid warning is given, the police send out cars and motorcycles, and go to phone boxes, while the superintendent takes charge at the station. A policeman ushers people into shelters, while off-duty police get to their posts. The map room is ready for action, and the police stand by.

The raid begins over deserted streets. Policemen telephone the location and nature of bombs dropped and the damage caused. After the all-clear is sounded, the Superintendent reports to Scotland Yard.