It happened all at once, and Eliza wasn’t even sure what she was seeing at first. As if called by a siren in the distance, all of the creatures froze, even the ones mere inches from Eliza’s boots. In one accord, they turned their heads, looking up and peering across the street, toward the top of another building several blocks over. Then, they all slithered back the directions in which they had come, crawling across the roof and back over the ledges, down the walls, and through the yard. It took Eliza a moment to get her feet to follow them, but she moved to the edge of the rooftop,...