At first the incursions were small. A couple of ears of corn here would go missing, or a small patch of potato wouldn't come to crop. Nobody worried overmuch - Mother Nature was always due her share of the harvest. Next, a lamb would go, or a calf. Still, nobody paid it much mind. Nature was ever a thief in the night.
Next, sheep and cows would disappear in the darkest hours. As the barrier weakened, They grew bolder and bolder. Night time disappearances turned to daytime thefts, and the people began to worry. They hustled the sheep in, they hustled the cows in, and they hustled each other inside. The old ways began to come back to them, as they shod their horses and cowered behind iron doors.
Still, They came. As the barrier broke, They came forward with pointed smiles and sharpened teeth. Iron doors weren't enough to keep the people safe, and they fled from their homes. Alas, Their weapons were in their music and their melodies broke open the night.