NORTH, EAST, SOUTH, WEST...
The offspring of Simon Tregarth, half earthling, half witch-brood, realized that they alone could perceive the four directions - for everyone else, there was no East!
It was a blank in the mind, a blank in legend and history.
And when new menaces threatened, the Tregarths realized that in that mental barrier there lay the key to all their world... somewhere to the unknown eastward must lie the sorcery that had secretly molded their destinies!