Something to keep your party on their toes.
The PCs are hired by undead to rid their village community of an invasive necromancer.
As the PCs make their way, wherever they are going, they spot two zombies. The zombies approach but before the cleric can turn them, one starts throwing coins at the PCs while the other pleads with them, unable to pronounce the letters "L" and "H" due to some missing gums. "Peeth issen...no 'arm...coin...peeth issen!"
If the PCs don't slaughter the two zombies immediately, they will eventually come to learn that the two were chosen to find help by their brethren. The zombies want to hire the PCs to rid their community of an unwanted pest. An opportunistic necromancer.
Apparently, a small benign community of undead have taken residence in an abandoned village, living out their undeath as peacefully as the undead can. Recently, a malicious necromancer has invaded the village, and plans to enslave the entire populace with his malignant spells, raising a small army.
The PCs must battle the vile necromancer, even as he animates the very folks who hired the PCs in the first place, to slaughter them.