Hans Daedalus has defected from East Germany to the West. Is it possible that his opacity equations live on after his death?
| Actor | Role |
|---|---|
 Michael BryantSam McInstrey | Sam McInstrey |
 Megs JenkinsEileen Gray | Eileen Gray |
 Peter SallisMajor Venables | Major Venables |
 Estelle KohlerMary Stannage | Mary Stannage |
 Richard HurndallSherborne | Sherborne |
 George CoulourisHans Daedalus | Hans Daedalus |
| EEve MortimerMadge Baxter | Madge Baxter |
| JJohn AtkinsonPerry | Perry |
| RRod BeachamSergeant Riley | Sergeant Riley |
| EElizabeth ChoiceWoman at Seance | Woman at Seance |