'Primeval' (4 Parts) 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.

Peter Davison (the Fifth Doctor) and Sarah Sutton (Nyssa), Stephen Greif (Kwundar), Susan Penhaligon (Shayla), Ian Hallard (Sabian), Billy Miller (Narthex), Romy Tennant (Anona), Marc Woolgar (Hyrca) and Rita Davies (Janneus)



Notes:
*Featuring the Fifth Doctor and Nyssa

*A Big Finish Audio Production