Professor Emil Keller has created a machine that can pacify even the most dangerous of criminals. But when the Doctor and Jo arrive at Stangmoor Prison for a demonstration, things start to go horribly wrong - especially when they discover that the Doctor's old enemy the Master is responsible for the machine.
| Directing | Timothy Combe | Director |
| Writing | Don Houghton | Writer |
| Writing | Terrance Dicks | Script Editor |
| Production | Barry Letts | Producer |
| Sound | Dudley Simpson | Music |
| Visual Effects | Jim Ward | Visual Effects |
| Costume & Make-Up | Bobi Bartlett | Costume Design |
| Costume & Make-Up | Jan Harrison Shell | Makeup Artist |
| Lighting | Eric Monk | Lighting Director |
| Sound | Chick Anthony | Sound |
| Art | Ray London | Production Design |
| Camera | Fred Hamilton | Camera Operator |
| Camera | Max Samett | Camera Operator |
| Editing | Howard Billingham | Editor |
| Editing | Sam Upton | Editor |
| Editing | Roger Harvey | Editor |
