Classic Doctor Who Season 21 Episode 10 Frontios: Part: 4

The Doctor and his companions, Tegan and Turlough, find themselves trapped on the planet Frontios, which is under attack by mysterious creatures that seem to originate from beneath the ground. As they try to figure out what is happening, they are caught up in a power struggle between the colony's leaders, Brazen and Range, and a rebel group led by Cockerill.

In the previous episode, the Doctor and his companions managed to escape from a collapsing underground tunnel, but Turlough was injured in the process. As they make their way back to the colony, they encounter some of the creatures and realize that they are actually a primitive life form that has been disturbed by the colony's mining activities.

Meanwhile, Brazen and Range are busy quelling the rebellion, which they believe is responsible for the recent attacks. However, Cockerill insists that the creatures are to blame and urges them to halt the mining operations. The Doctor, Tegan, and Turlough soon find themselves caught in the middle of this conflict as they try to convince everyone to work together to find a solution.

As they explore the planet further, they discover a hidden chamber that contains ancient technology that may hold the key to stopping the attacks. However, they are intercepted by a sinister figure known as the Gravis, who seems to be controlling the creatures from a distance. The Gravis is revealed to be a sentient life form that was once a part of the planet's core, and it has been using the colony's mining operations to expand and manipulate its own body.

With the help of Cockerill and his rebel forces, the Doctor devises a plan to destroy the Gravis and restore balance to the planet. However, things quickly spiral out of control as the Gravis fights back and the colony is plunged into chaos. In the end, it will take all of the Doctor's ingenuity and bravery to save the day and ensure that Frontios can thrive once again.