A strange creature forces its way into the TARDIS, steering it to a white void occupied only by the ruins of an old building and a spaceship. This empty space is a gateway to the past and future. The creature responsible for taking them there is Biroc, a member of the enslaved race known as the Tharil. The gateway offers the only exit from E-Space, but the void is contracting. Are the Fourth Doctor and his friends fated to spend eternity in E-Space? What final shocking revelation awaits the Doctor?