26. Primeval

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...

31 out of 76 (40.8%) raters say this story requires a previous story.