From the introduction:
During Drakonheim’s golden age, the city planners designed an extensive sewer system beneath the city. The wealthier homes connected directly to these sewers, while the poorer folk used public latrines. In their time, the sewers were marvels of engineering, but as the empire declined they fell into disrepair.
A few hundred years ago a small band of goblins entered one of the drainage pipes and found the sewers to be a perfect home. They have been thriving and multiplying ever since, and now thousands of goblins live beneath the streets of Drakonheim.
Some goblins emerge from the sewers to explore the world beyond. The Savage Worlds Drakonheim Companion presents them as a new playable race with new Racial Edges. Goblins also feature prominently in the first chapter of the Heroes of Drakonheim adventure. The heroes trudge through goblin-filled sewers where they meet the (potential) helpful Gozy the Quiet, and the final encounter pits the heroes and a murderous corpse-selling goblin name Korth Fat Rat.