The Doctor tracks the missing scientists to Irongron's castle, where Linx is using them to repair his spaceship and construct advanced weapons for Irongron.
| Name | Type | Role | |
|---|---|---|---|
| Robert Holmes | Writer | ||
| John J. Carney | Guest Star | ||
| Bill Monks | Guest Star | ||
| Dudley Long | Guest Star | ||
| Donald Pelmear | Guest Star | ||
| June Brown | Guest Star | ||
| Alan Bromley | Director |