Castrovalva: Part 1

S19, E1: The first appearance of Peter Davison as the Doctor. The universe has been saved, but at the cost of the fourth Doctor's life. The newly-regenerated fifth Doctor must rely on his friends to survive as the regeneration threatens to fail. Adric has been captured by the Master, who is taking advantage of the Doctor's weakened state to ensnare him in an elaborate trap which threatens to destroy his mind.