MI5 suspects British atomic research has been infiltrated and asks Foyle to look into whether a Russian spy network could be at work in the heart of London.
| Name | Type | Role | |
|---|---|---|---|
| Anthony Horowitz | Writer | ||
| Stuart Orme | Director | ||
| Honeysuckle Weeks | Actor | Sam Wainwright | |
| Ken Bones | Actor | Max Hoffman | |
| Gabrielle Lloyd | Actor | Maureen Greenwood | |
| Steve Wilson | Actor | Duty Police Officer | |
| Tim McMullan | Actor | Arthur Valentine | |
| Bush Moukarzel | Actor | Soldier at Vlessing's | |
| Daniel Weyman | Actor | Adam Wainwright | |
| Stephen Boxer | Actor | Professor Fraser | |
| Emma Lowe | Actor | Jane Conway | |
| Nathan Gordon | Actor | Marc Vlessing | |
| Joe Duttine | Actor | Frank Shaw | |
| Peter O'Byrne | Actor | Town Hall Official | |
| Jennifer Hennessy | Actor | Ruth Shaw | |
| Kate Duchêne | Actor | Helen Fraser | |
| Georg Nikoloff | Actor | Russian Agent | |
| Christopher Fulford | Actor | Det. Supt. Cranborne | |
| Ellie Haddington | Actor | Hilda Pearce | |
| Jeremy Swift | Actor | Glenvil Harris | |
| Sam Clemmett | Actor | Jack Shaw | |
| Patrick Joseph Byrnes | Actor | American Scientist | |
| Michael Kitchen | Actor | Christopher Foyle | |
| Anne Kent | Actor | Woman on Stairs | |
| Nicholas Jones | Actor | Sir William Chambers | |
| Philip Judge | Actor | Cyril Conway | |
| Gyuri Sarossy | Actor | Tomasz Debski | |
| Dylan Charles | Actor | Aleksei Gorin | |
| Stephen Swift | Actor | Radiation Soldier |