That white spot arises, of course, from the single dry crystal of poison in the syringe that Edgar discovers in the work room. After the syringe is accidentally crushed, and the crystal dissolved in rainwater, it could have just soaked into the ground and been forgotten. In fact, during early drafts of the novel, that is exactly what happened—the important thing, for me, was that no physical evidence remain. I wanted Edgar to have to act in the absence of proof. But during the final drafts, it also occurred to me that, potent as it is, even a tiny bit of that poison would leave a mark on the world. That in turn opened the question of what such a mark might be. The answer that made sense to me was not any straightforward sign of poison, or death, but of inexplicable strangeness, of half-life, which was in keeping with Edgar’s experience. A white dandelion appeared in my imagination.
This is typical of how writing works for me. I don’t plot things out ahead of time in great detail. Instead, I set a direction and write toward it. Certain elements tossed in during early drafts become increasingly significant as I revise (and certain other elements lose power and fade away). In this case, every time I reexamined that passage, I wondered: “What about that crystal in the syringe? Why was it there? What happened to it anyway? Is it in the groundwater—in the well? Is it in the creek? Has it been neutralized somehow? Is it just plain gone?” Since I couldn’t shake the question (I tried), I had to answer it.
When that white dandelion appeared in my imagination, it struck me as just the right “residue”—a ghostly plant. I also knew Edgar would find the mark and interpret it as evidence that he hadn’t simply imagined everything, despite being awash in the mundane details of the everyday world. Knowing Edgar, I knew he would obsess about that white spot, conclude it was a stain on his world, try to eliminate it. More importantly, I knew it would give Edgar a tiny bit of tangible evidence of what happened to his father—but evidence only to Edgar.
Many such story details appeared during the initial writing, were propagated throughout the story in the middle drafts and settled into place during the final revision. Mostly, readers don’t (and shouldn’t) notice those details, but they are essential to long-form fiction, each one a strand in the braid that holds the novel together. Only a few—like the white patch—are ever intentionally in the foreground.