Back in the forgotten past, when Alarielle with the other gods ruled the Realms, her children plant a great tree that would serve as beacon and meeting point for other children of Alarielle. But then Nurgle's armies and his corruption arrived and drove Sylvaneth away. Corrupting the great tree into something horrible. But the age of Chaos was not about all the Gods working together. And thus Khorn armies descended upon this accursed tree and destroyed it together with Nurgle army. Soon Khorn army departed towards more slaughter and leaving the broken tree behind. Not relasing what those putrid spawns of Nurgle where "growing" in its roots.
Now a new warband of Khorn worshippers come to this Heartwood, yet there leader knows that something is hiding deep within it. And like all the powers before, this one will also be brought to his will. Whatever it might be.