Doctor Who and the Underworld

Exploring the very edge of the known universe, the Fourth Doctor, Leela and K9 discover a group of astronaunts searching for the lost gene bank of the Minyan race. During the perilous voyage, the astronauts' craft plunges into the heart of a recently formed planet, wherein an awesome secret is hidden.

How will the Minyan quest end?

What must the Doctor wrest from the Heart of the Oracle?