A Map of the World
During the investigation, Sam draws a neat little map of Knocknaree, and Rob hates it. He says, "It got on my nerves for reasons I couldn't quite define. It was the perfection of it, I think, the fragile enchanting detail" (10.49). Why does Rob hate it? Maybe because Sam has given order to the chaos in Rob's head, chaos Rob can never hope to sort out. Or maybe it's Sam's ability to hunker down and focus, to see clearly while Rob fumbles around grumpily and emotionally.
We only see the map twice—once when Sam draws it, and again when he takes it down, at which point we're shown that "his map of Knocknaree was starting to curl at the edges" (25.6). In a way, so has Rob's life by this point. He's lost his career and his friends. It's mostly his fault, but he probably wouldn't be such a hot mess were it not for what happened to him at Knocknaree. And insofar as his entire life has been changed by this town, when we see the map of the town worn down, we're reminded of how worn down Rob is, too.