Category: - The Dark Inventory
The clue is in the title.  The wise old Vapour Queen has been given the worst birthday present of all in the form of a stab wound via the very thing she helps.  Gaunt the Cat has been tricked into delivering the blow by the Sunken Vast, a jealous and heavy spirit of depth.  The duality of fleeting importance and deep abyss ridden waste.  

The naivety and wisdom of age vs the naivety and wisdom of youth.