From the announcement:
War rages across the Mortal Realms. The focal points of the first great battles were those magical portals known as Realmgates, doorways through reality with immense strategic importance. The wars over these were brutal and bloody, and while Sigmar’s glorious Stormcast Eternals can lay claim to victory, it was not quite the all-conquering victory for which they might have hoped. It was not long before the Dark Gods marshalled their counterattack – and none were so febrile and repulsive as those of Grandfather Nurgle…
Warhammer Age of Sigmar: Blightwar is a great-value boxed set, featuring 32 plastic Citadel miniatures split across the armies of Nurgle and the Stormcast Eternals. It focuses on the Blightwar – Nurgle’s dastardly plan to befoul the realm of Ghyran using his Grand Cultivator Horticulous Slimux, and the heroic attempts to stop him by Neave Blacktalon, deadly huntress and swift-footed assassin of the Stormcast Eternals.