Doctor Who and the Underworld — Terrance Dicks

Exploring the very edge of the known universe, the Doctor, Leela, and K9 discover a group of astronauts searching for the lost gene bank of 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?