The Fifth Doctor visits his old friend David Gosthorpe, a scientist who made some of the greatest inventions in the universe. David's inventions are threatened when his evil sister starts to use them for her own pleasure. With Nyssa trapped inside her evil games, the Doctor must find a way to stop Ellen Carter's new power from spiraling out of control.
- Nyssa asks the Doctor hopefully about tea and cake.
- The Doctor says he's from UNIT to avoid being questioned about a death.
- David Gosthorpe died of a stroke in Naples, Italy in 1987.
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