The Knock

Customs and Excise discover a plot to smuggle heroin into England from Jamaica via mail, illegal plane landings, and a Columbian woman driven to smuggling by her debts.

Child pornography is being smuggled from Thailand. Adams tries to stop it, and Ralston investigates the unidentified plane.

George Webster gets a hold on Birch while the team discover a heroin-smuggling group linked to a Chinese restaurant in London's Chinatown, run by a Triad syndicate.

Ralston discovers products made from endangered species, as a spilt container reveals animal horns. Meanwhile, Barton begins smuggling gold for Webster, and heroin shipments arrive from Hong Kong.

Andreotti inadvertently begins investigating an international drug smuggler. Diplomatic issues bring Ralston's investigation to a halt. Birch realises his mistake in working for Webster and tries to escape but it's not so easy.

The team follow Barton as he brings gold illegally into the country. Webster decides to up their smuggling operation and take bullion from all over Europe. Andreotti is successful with the Mullvany case.

Webster cuts Barton off, so he tries to escape but is chased into the London Underground, where he commits suicide. Birch and Beverley Webster are caught at Dover with the gold hidden in the car bumper.