Deep in the marshes the Tree of Cognizance feeds on whatever living creatures come near it, using very powerful illusions and brute strength. It’s fruits are prized by those that understand the powers they offer.
Evil gives birth to many foul creatures, of these creatures the Negasek have emerged from a womb of darkness and terror. These powerful insect-like creatures radiate the dark force that gave birth to them, born of sheer negative energy, nearly dripping with the foulness of their diabolic nature.
The PCs are sent with a diplomat to another country to protect him and do his bidding. There may be some espionage, rescuing, downright bullying, etc. Could make a nice medieval, special operations background.