When a wizard named Mendalus develops a spell that summons an obedient woman named Catherine--exactly like any other summoning spell--it creates chaos in the wizard-metropolis of Meltheria, as many interested parties struggle to understand the nature (and legality) of the Catherine spell, while vast fortunes hang in the balance.
Darklings are a kind of Halflings living in the sewer of medium to large cities.
Even though they smell badly and are quite dirty, Darklings are friendly and clever.
They try to limit the knowledge about their existence to only a small number of trustworthy persons, including player characters.
Darklings trade in information. Money, weapons and magical items have no value for them. This is why they hide beneath the sewer grates, listening to all that is said in the city above.