Carrying a complement of Stena refugees, the TARDIS buffets under fire from the Haxeen, the predators of the former species. As the time ship is immobilised and the Haxeen try to break in, the Doctor and Peri go over what they know, Peri asking how it helps them one "bit".
An epiphany strikes the Doctor and he realises that the Stena give off a unique binary signal that the Haxeen feed off of. As the Doctor floods the vortex with a binary substitute, the now sated multi-dimensional aliens backing off. With a smile, the Doctor sets course for a new home for the Stena. Preferably one that's virtually indestructible.
- The Haxeen are classified by the Doctor as one of the few aluminium-based lifeforms he encountered.
- Bits are the basic measure of information or data.