To escape from the volcanic eruption on Dulkis in the previous episode, the Doctor takes the TARDIS out of normal time and space.  The TARDIS crew find themselves in an strange void.  After the TARDIS explodes they find themselves in the land of fiction.  A man known as the Master (but not the Time Lord Master) rules the area with help from a Master Brain computer.  The Master wants to escape and he wants the Doctor to allow him to do so by taking his place.  The Doctor engages the Master in a battle of wills while Zoe and Jamie overload the Master Brain causing the White Robots to destroy it.