A less racist, more trippy take on The Toymaker and ultimately a literal write-off
The Second Doctor and his companions, Jamie and Zoe, escape the volcanic eruption on Dulcis (and heartless mass-murder of all remaining Dulcian protagonists) by taking the TARDIS to The Land of Fiction, a parallel dimension of fictitious characters.
Controlling the parallel dimension is world-class plagiarist and alleged world-builder and writer of original works, The Master (not that Master), aka “The Master of the Land”. And controlling The Master (still not that Master) is a great intelligence (sort of like the Great Intelligence) and master-computer desiring world-domination (sort of like WOTAN) called The Master Brain.
The Master’s growing old, though, and wanting a fresh mind to take his place, The Master Brain now has its sights set on The Doctor.