The Knock — Season 4

The team get a new boss in David Ancrom. Meanwhile, drug baron Frankie Johnson and his partner, American wheeler-dealer Greg Taylor with a sideline in plutonium smuggling, become a headache for the team.

Johnson and Taylor arrange to have the courier killed, as he returns from South Africa suffering from radiation sickness. The team are in a deadly race against time as ultimatum from an arms dealer means trouble.

As fellow conspirators start turning up dead and the Customs net starts to close in on him, Taylor panics and desperately attempts to close the deal for the bomb.

An Algerian heroin smuggling ring is exposed after an illegal immigrant is found hiding in the luggage compartment of a coach. Ancrom investigates a drug baron's wife suspected of continuing business.

Christie's undercover operation is threatened when the Algerians suspect they've been betrayed, putting Christie in danger. The rest of the team are also involved in a group who smuggle endangered animals.

Ancrom discovers Ralston made a deal with Toni Maxwell, in return for Christie's whereabouts. An operation on a gang of crooked airport baggage-handlers goes like clockwork, until their psychotic leader escapes.