This episode is taken from the Doctor Who: The Fourth Doctor Adventures Series 9 Volume 1, and is available free to Big Finish Newsletter subscribers in January 2020.
9.2 Chase the Night by Jonathan Morris
The TARDIS lands in an alien tropical rainforest at night where the Doctor, Adric and Romana discover a set of rails stretching through the undergrowth. These tracks carry a long-crashed spaceship that’s been converted to run along them like a train.
The ship has to keep moving because only the night-side of the world is habitable. The sun on the day-side burns so hot that everything on the surface is turned to ash.
But the stress and strain of the constant movement is beginning to take its toll on the ship. Parts are starting to break down, and the relentless heat gets ever closer - but the greatest danger may be on the inside...