The crooks in London know how it works. No one carries guns and no one resists the police. Then a new gang appears that go one better. They dress as police and steal from the crooks. This upsets the natural order of the police/criminal relationship and the police and the crooks join forces to catch the IPOs (Impersonating Police Officers), including an armoured car robbery in which the police must help the gangs to set a trap.

Three criminals plan to break out of prison the day before their release in order to carry out a daring jewel robbery, intending to establish the perfect alibi by returning to jail afterwards. First however they must get out, a task made more difficult by a new, stricter prison officer.