At Stangmoor Prison, the Doctor and Jo watch a demonstration of the Keller Machine which can extract evil impulses from criminals. But the experiment goes wrong and a man dies.
| Name | Type | Role | |
|---|---|---|---|
| Don Houghton | Writer | ||
| Roy Purcell | Guest Star | Chief Prison Officer Powers | |
| Ernesto Macias | Guest Star | ||
| Pik-Sen Lim | Guest Star | ||
| Raymond Westwell | Guest Star | ||
| Clive Scott | Guest Star | ||
| Timothy Combe | Director |