Recruited by the Russians during their days at Cambridge, three young Englishmen rise to become high-ranked MI5 agents until their exposure in 1949.
| Actor | Role |
|---|---|
 Anthony BateKim Philby | Kim Philby |
 Derek JacobiGuy Burgess | Guy Burgess |
 Michael CulverDonald Maclean | Donald Maclean |
 Ingrid HafnerAileen Philby | Aileen Philby |
 Elizabeth SealMelinda Maclean | Melinda Maclean |
 Richard HurndallSir Stewart Menzies | Sir Stewart Menzies |
 Philip StoneFarquesson | Farquesson |
 Peter VaughanPhilby's Control | Philby's Control |
 Arthur LoweHerbert Morrison | Herbert Morrison |
 Bernard ArchardGraves | Graves |
 Oliver Ford DaviesPattterson | Pattterson |
 Robin HooperReed | Reed |
 Patrick HoltPeterson | Peterson |
| DDavid MarkhamSkardon | Skardon |
| BBarrie CooksonHelenus Milmo | Helenus Milmo |
 Hugh MortonMarcus Lipton | Marcus Lipton |
| TTony SibbaldReporter | Reporter |
| RRichard HamptonMajor Sansom | Major Sansom |
| AAnthony LangdonVolkov | Volkov |