Injured after a shoot-out between his old nemesis the Master and the Ogrons, slaves to the evil Daleks, the Doctor sends a message to the Time Lords, asking them to pilot his TARDIS and follow the Daleks to their new base. After he slips into a coma, it falls to his assistant Jo Grant to explore the planet where the TARDIS finally materialises.
Not only must the Doctor contend with the Daleks' new stratagem, but he must try to stop them unleashing a plague that will exterminate all organic …