When the TARDIS malfunctions, it and its travellers land on Earth at the size of insects. They uncover a murderous plot involving a new insecticide, but how can they stop the crime in their miniaturised condition?
| Actor | Role |
|---|---|
 William HartnellThe Doctor | The Doctor |
 Carole Ann FordSusan Foreman | Susan Foreman |
 Jacqueline HillBarbara Wright | Barbara Wright |
 William RussellIan Chesterton | Ian Chesterton |
 Alan TilvernForester | Forester |
| FFrank CrawshawFarrow | Farrow |
| RReginald BarrattSmithers | Smithers |
| RRosemary JohnsonHilda | Hilda |
| FFred FerrisBert | Bert |