Note: Exclusively available from the Big Finish website until July 31st.
The TARDIS is going underground. When the Doctor and Romana find themselves buried beneath the surface of an alien world, they're soon swallowed up by a giant burrowing machine. This is where the inhabitants of this planet live — in huge, constantly moving, Drill-towns, chewing up the fuel and resources of the planet in order to survive.
But something else lurks in the earth. Something that feeds on the Drill-towns. Something that is relentless and will not stop.
The Silex are hunting.