Slaad of the North Forest - Resolved

The party killed a number of Blue Slaad and tapoles in the forest north of Craven's Rest. The creatures seemed to have hatched from a troll that had a large egg sac in its chest. In the lair of the troll they found a unusual skeleton that showed damage to its chest cavity that suggested it had an egg sac as well.
Among the bones, they found a pouch of coins minted over 200 years ago in Port Oruss. The corpse was wearing a signet ring with a stylized "H" and a faint magical aura consistent with an item used as a key. They also found a pouch of lead pellets that Trevor recognized as Goblin currency.
How did the troll get infected with eggs? Where did this strange corpse come from? Where did it get such odd items?
Dael revealed that the corpse was actually that of a Hobgoblin. Lucas discovered that the signet ring bears the symbol of Invarnack, a mage of some renown who wrote the tome that Andres used to identify the Slaad.
On the trip home from Port Oruss, the party met with a group of traveling herbalists who had taken in a pair of humans who the part recognized from a scavenger camp. They had been attacked by a Blue Slaad where one of their group had been killed and two others injured. The Slaad dragged the corpse and one injured person north into the forest.
After speaking with the Rangers stationed in Craven's Rest, the party learned that the northeast hunter's camp had recently gone quiet. They went to go check on the inhabitants there, with Ellia acting as their guide. They discovered multiple slaad there, three Red and one Green. They also found a trail of another slaad, a Blue that was returning to the "Tower" (as Ellia read from the Green's mind before it died).