The TARDIS lands on the jungle planet Spiridon, where the Doctor has fallen into a coma. Before collapsing he has requested the Time Lords to pilot the TARDIS, so he and Jo can follow the Daleks to their base. Jo learns the Daleks' base has been located on Spiridon where they are attempting to discover the secrets of Invisibilty and create a bacterial virus in their goal of universal conquest. When the Doctor recovers, he and Jo are joined by a task-force of Thals and a native Spiridon named Wester. They not only set out to stop he Daleks' evil plot, they also discover an army of 12,000 Daleks are in suspended animation and are waiting to be revived to begin their universal conquest and claim themselves as the supreme rulers of the galaxy.