| Focuses on Bernard Samson (Ian Holm), beginning with his search for the "mole" that threatens the Brahms Network in East Germany. Samson is sent to Berlin to bring out a Brahms agent. He is then sent to Mexico to try to persuade a KGB major (Gottfried John) to defect, using his childhood friend Verner Volkmann's wife Zena as bait. After it appears another traitor is working at London Central, Samson himself becomes one of the prime suspects. |
| Name | Character | Episodes |
|---|---|---|
| Ian Holm | Bernard Samson | 13 |
| Gottfried John | Erich Stinnes | 13 |
| Hugh Fraser | Giles Trent | 13 |
| Michael Degen | Werner Volkmann | 13 |
| Frederick Treves | Frank Harrington | 13 |
| Michael Culver | Dicky Cruyer | 13 |
| Anthony Bate | Bret Renssalaer | 13 |
| Gail Harrison | Tessa Kozinski | 13 |
| Jeremy Child | Henry Tiptree | 13 |
| Amanda Donohoe | Gloria Kent | 8 |
| Michael Aldridge | Silas Gaunt | 3 |
| Gottfried John | 3 | |
| Michael Mellinger | Rolf Mauser | 2 |
| Peter Vaughan | David Kimber-Hutchinson | 1 |
| Annette Crosbie | Mrs. Miller | 1 |
| Ralf Wolter | Juri Roster | 1 |
| Dieter Kirchlechner | Walter Von Munte | 1 |
| Bruno Dietrich | Paul Biedermann | 1 |