Senior officials in the British, American and Russian governments all receive the same cryptic and unsigned message - "I Can Destroy The Sun". What can it mean?
| Actor | Role |
|---|---|
 Maurice DenhamDr. Lunn | Dr. Lunn |
 John RobinsonLloyd Crichton | Lloyd Crichton |
 Robert AyresBoardman | Boardman |
 Leslie SandsSuperintendent Travers | Superintendent Travers |
| JJan ConradIgor Petrov | Igor Petrov |
 John BarronHenry Walpole | Henry Walpole |
 Robert JamesJames Cartright | James Cartright |
| JJennifer WrightMary Harkness | Mary Harkness |
| PPaddy WebsterHelen Dawson | Helen Dawson |
 Carmel McSharryBella | Bella |