Martha was a child when she saw a gnome for the first time. It was punting across a pond, sitting on an empty plastic bottle, and turned to face her for a moment. His eyes were sewn shut, and it seemed like he never had a mouth, with only a very small strip of blank skin under its nose.
At first she believed other people that she had imagined it, but over the years she saw more of its kind, usually one of a kind, sometimes two together. This did not happen so often that Martha could identify individuals, but often enough to notice there were differences in their faces, or just how bent their back was. The gnomes always ignored her, not like they did not notice her, but as if they could not possibly have any business with her, nor she with them.
She learned that people did not take her seriously when she talked about the gnomes, but since she wanted to know if anybody else saw them, she reduced her efforts to talking about more-things-between-heaven-and-earth spirituality, and only if someone else brought it up first. Mostly everything was shrugged off, and even those people who said they had seen something they could not explain never described it in any way like Martha's gnomes. She did not quite know if she should feel honoured, or worry that she was only imagining things.
When, after decades, she noticed that their habits seemed to change - she saw them less frequently, but when she did, they were in groups - she grew nervous, and talked about gnomes, ghosts and fairies more. It made sure that people who had known her all her life remembered the stories she used to tell.
When a dead body with its eyes and mouth sewn shut was found, they knew who would know about it. The old spinster obviously had lost her mind completely.