Hunter, head of the Section, requires the services of his best operative, David Callan. Callan had been 'retired' from the service due to his growing conscience, disrespect for orders, and concerns about the people he was ordered to eliminate. Callan now working as a bookkeeper, a job he despises, is offered to be reinstated into the Section if he kills Schneider, an international arms dealer.

Under threat of being placed in a red file, Callan is coerced into helping the Section hand over an ex-SS officer, Strauss, to the Israelis.

Callan must stop an old friend, Clarke, from going back to Africa, where he was training mercenaries, else Hunter will have Clarke killed.

Two CIA agents request the help of Hunter's Section in killing a Chinese agent, who has been trading in nuclear secrets. But his real mission in England is to kill Hunter.

Callan is lured into going to Berlin, where Hunter wants to use him as a sacrificial lamb to facilitate the planting of a British mole.

Hunter wants Callan to stop a blackmailing Lord from selling the negatives used in the blackmail to all and sundry.

When somebody beats Lonely up, and Callan finds out who it was he turns the table on Hunter.

The Section's new Hunter has Callan pulled from the field.

Callan must prove that a young biochemist is not giving information to the East.

Callan apparently turns renegade. A ruse to trap the head of a ‘pipeline' for smuggling foreign agents and defectors out of the country.

Callan must use the wife of a rocket scientist as bait to lure the same scientist to Britain.

A freelance German mercenary organisation who specialise in eliminating foreign security sections have their sights set on the Section.

After Hunter's death Meres and Calln must fetch the new Hunter from East Germany.

Callan must retrieve a microfilm from a spying medium.

Calln must find everything out about the past of an influential politician.

The French O.A.S. carry an internal war into England. Callan and Meres must sort out the mess.

Callan and Meres must catch the controller of a ring of spies before he can leave the country with the information the ring has gathered.

Callan and Meres must secure the safe of a ship that was sunk during World War Two. It contains a list of Third Reich collaborateurs and puppets. A survivor of the ship tries to stop them.

Callan must stop fashist agitators from killing the Chinese Ambassador.

Security wants a retired brigadier of the British army to be stopped from accepting a job offer from a sultan, deadly force is requested.

Callan brings confusion into a Russian spy network.

Callan in brainwashed into believing that Hunter is the leak in the Section and that he has also killed Lonely and framed Callan for murder. In his drugged state Callan kills Hunter and is shot down by Meres.

The new Hunter cannot decide if Callan is to return to the Section or not.

When Cross kills an innocent bystander it's up to Callan to cover for him, but even he cannot decide if it was an accident or murder.

An exchange of captured agents with the Soviets goes sour.