From the publishers website:
Sources of purity, the waystones help maintain the Winds of Magic. If they can be corrupted, the Dark Elves will strike at the source of their sworn enemies’ powers, breaking an age-old stalemate once and for all.
The Fourth Waystone is the fifth Battle Pack installment of The Enemy Cycle, a linked expansion series for Warhammer: Invasion, a card game of intense warfare, clever kingdom management, and epic questing.
This 60 card pack contains 20 different never-before-seen cards designed to augment existing decks and add variety to the Warhammer: Invasion metagame.