Those who hunt by night will tell you that the wildest, most vicious of all animals is the tiny shrew.
The shrew feeds only by the dark of night. He must eat his own body weight every few hours or stave to death. The ravenous shrew eats everything, bones, flesh, marrow… everything.
Intro from Attack of the Killer Shrews 1959
A plague is spreading trough the lands, the plague is actually an old woman carrying a stick. She walks from farm to farm spreading the plague. Can the PCs stop her without getting infected.