From publisher blurb:
Kivuli, the villain from BR-1, found and was nursing the egg of the dragon that chased the dwarven cleric through the gate (detailed below). He was in hopes of hatching and controlling the young black dragon. The PCs either killed or drove off the magic-wielding kobold in their adventure.
The caves in which the above adventure took place are the original creation of dwarves. They previously created a gate to the dragon lair in the swamps in order to finish the job of slaying the mated pair of dragons.
The male dragon returned to the lair to find his mate and her nest gone and his treasure looted by the nasty dwarves. He would take his revenge!
He is now aware that he has a hatchling in the old lair. He is healed and can finally get his complete revenge, save his youngling, and perhaps retrieve some of his hoard! Of course, provided the PCs didn’t slay the hatchling. Nagareth seeks revenge either way.