Forty: Volume 1

 was a full cast audio anthology released on 4 January 2022 by Big Finish Productions. It featured Peter Davison as the Fifth Doctor, Matthew Waterhouse as Adric, Sarah Sutton as Nyssa and Janet Fielding as Tegan Jovanka. This acted as a celebration of forty years since the Fifth Doctor's first regular appearance, and began an overarching narrative for the series, with two versions of the Fifth Doctor "jumping time tracks", or being pulled along his time stream, to different points within the same incarnation.

Secrets of Telos also acted as a sequel to TV: The Tomb of the Cybermen (and AUDIO: Return to Telos, by extension), by bringing the Doctor, Tegan and Nyssa to the Telos system, mere hours after the Second Doctor, Jamie and Victoria departed, to deal with the aftermath on Hopper's rocket, alongside Parry.

Publisher's summary
1. Secrets of Telos by Matt Fitton

Professor Parry's expedition to the tombs of Telos was hardly an unmitigated success. The handful of survivors limp home in a spaceship...unaware that the deadly peril they faced from the Cybermen is not yet banished.

Into this situation stumble the Fifth Doctor and his friends Nyssa and Tegan - and they're soon in a deadly fight for their lives.

Except things aren't quite that simple - something odd is happening to the Doctor. He's suddenly in a different part of his own timeline inhabiting his future self with no idea of why or how this has happened.

Who is bouncing him through time? And what could they possibly want?

2. God of War by Sarah Grochala

The Doctor is still being jolted through his own timeline, and has now found himself with Nyssa, Tegan and Adric in ninth century Iceland near a Viking settlement on the edge of a volcano. A settlement whose leader has just found a god in the ice.

The TARDIS crew are soon in a battle with the fearsome Ice Warriors. There are a lot of lives to save... and not just those of their new friends.

The Doctor's about to find that his biggest battle may be with his own conscience.