The TARDIS make a bumpy landing on Karn, home of the legendary Sisterhood. There the Doctor encounters his old acquaintance Ohila, who denies all suggestions of involvement in recent unusual activities on Earth.

The Doctor, Alex and Brandon move on to the planet Escalupia, a medical hub for Earth’s First Great and Bountiful Human Empire. There they find squalid living conditions and sinister, hovering drones preying upon the populace. Why does everyone fear doctors, and who is the Angel they seem desperate to see?

When Alex is captured by the drones, the Doctor discovers that the slums are test labs for huge medical companies, with the humans as lab rats. Furthermore, the mysterious Angel is someone they’ve encountered before - someone well known to Ohila...

The stakes are high, as the travellers and the Sisterhood fight to end an injustice and escape with their lives.