When a mysterious balloon lands in a bird sanctuary, a scientific investigation led by the Doctor and UNIT reveals a threat from a universe of anti-matter. An ancient, exiled Time Lord named Omega is using a black hole to drain cosmic energy and kidnap humans, seeking revenge against his own race. To combat this crisis, the Time Lords break the laws of time to allow the Doctor's past incarnations to work together. The Doctors discover that Omega has lost his physical form and exists only through mental will, making him too unstable to be reasoned with. By tricking Omega into touching a recorder made of normal matter, they trigger an explosion that destroys his realm and restores the Universe. As a reward for his bravery, the Time Lords finally lift the Doctor's exile, restoring his knowledge of time travel.