A woman walks into a village police station and reports a crime that has yet to happen. Her boyfriend helped plan it when he was in prison. Now he's been released, he wants it stopped, but if he tells the police, they might charge him with conspiracy - and the underworld would do what they always do to snitches. Constable Fred Lawson takes down the details. His station sergeant reckons it's a fantasy but as the woman said they'd use bombs, he reports it up the line. Fred is ordered to persuade the boyfriend to become their inside man; he agrees providing they grant him immunity from prosecution. Fred must find out when, where and how the crime will be committed and inform the authorities. The Prime Minister has made it quite clear: the hostages must not be harmed; the ransom must not be paid.