Tendrils of brown clawing at the setting sun were the first sign. People wrote it off as a little incoming rain, if they noticed at all.
The second sign was an odd smell, perhaps best described as a ghost that was once a tree. People noticed this; the sensitive felt their eyes water, and the barely felt scent caused the short of breath to huff a bit. Authorities, when consulted, insisted that nothing was amiss.
Finally, a veil descended upon town, like mist. It was thick enough that the first few cars to emerge from behind it had their headlights on.
No more came.
The people were found where they lay, curled up in bed, on their couches, slumped in chairs at restaurants. They had not been suddenly overcome; cars were pulled over, loved ones were tucked in. And, aside from a few at the very edge, and those who had been away, the entire population of 817 souls never stirred again.