The TARDIS is drawn into an empty white void, somewhere between universes. But they are not the only ones trapped there.

When Rorvik learns that Romana is a time sensitive, he takes her prisoner, forcing her to find a way out of the void. The Doctor attempts to discover what lies beyond the mirror.

While Biroc leads the Doctor to a view of the Tharil's lordly past, Romana learns more about the damaged freighter and the coldheartedness of its crew. Meanwhile Commander Rorvik, confounded by the time mirror inside the universal center gateway, ignores evidence that it's no simple mirror and decides to blast it, imperiling the lives of everyone.

The Doctor deduces that the freighter is a slave ship loaded up with Tharils to be sold as time machine components, but the immense weight of Rorvik's damaged ship, designed to contain the Tharils, is now collapsing the fragile void of the micro-universe in which they're all stuck, pulling everything inside ever closer.