Doctor Who: The Companion Chronicles: The Invasion of E-Space (5.4)

Trapped within E-Space, the Doctor, Romana and Adric are searching for a Charged Vacuum Emboitment - the gateway back to our universe. It's like looking for a needle in a haystack...

Then, by pure chance, a brand new CVE rips into being. Its makers are The Farrian, a warlike race who possess the technology to break into E-Space. But they have come to invade and plunder this new territory, and the riches of the planet Ballustra are their first target...