Primeval

In 2001, Primeval was released by Big Finish Productions.

Cover blurb
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 Arc of Infinity.