Ep 14. The Green Death, Episode 6

The Doctor and Jo Grant travel to the small Welsh mining village of Llanfairfach to investigate a mysterious sickness that has been affecting miners in the area. Upon their arrival, they discover that the disease is caused by a toxic green slime that is being produced by an abandoned chemical plant owned by Global Chemicals. The plant is being run by a ruthless manager named Stevens who is willing to do anything to protect the company's reputation, even if it means endangering the lives of the entire village.

As the Doctor and Jo investigate further, they discover that the green slime is not only toxic to humans but also to a new species of giant maggots that have been bred by Global Chemicals in an attempt to develop a new protein source to solve world hunger. The Doctor and Jo team up with a local environmental activist named Professor Clifford Jones to try and stop Global Chemicals from releasing the giant maggots into the wild, which would have catastrophic consequences for the planet.

Meanwhile, Jo becomes enamored with Professor Jones, causing tensions to rise between her and the Doctor who is fiercely protective of her. However, their personal drama takes a backseat as they race against time to stop Global Chemicals and save the village from destruction.

The Green Death is a poignant episode that deals with themes of corporate greed, environmentalism, and the consequences of unchecked scientific advancement. It is also notable for being the final episode of the Third Doctor's era and marks a major turning point for the show. The episode features strong performances from Jon Pertwee as the Third Doctor and Katy Manning as Jo Grant, as well as an excellent supporting cast that includes the late great actor Nicholas Courtney as Brigadier Lethbridge-Stewart. The Green Death is a must-watch episode for Doctor Who fans and is widely regarded as one of the best episodes of the classic series.