Featuring Peter Davison as the Doctor and Sarah Sutton as Nyssa, written by Lance Parkin.
Nyssa will die at dawn, and the Doctor doesn't even know why.
To save her life, he must make a desperate journey to the only place in the universe where a cure might exist.
When even that fails, the Doctor has a choice let Nyssa die, or make a deal with the devil. After all, the road to hell is paved with good intentions.
This story takes place between "Time-Flight" and "The Arc of Infinity."