A killer wielding poisonous green beans terrorizes a small Canadian town Agatha Treadway has done her own preserving ever since the day her husband was done in by a can of supermarket tomatoes. And after four vigilant decades canning everything from peaches to spinach, it is her own green beans that kill her. Inspecting the fatal jar, Janet Wadman finds it has been tampered with, so that toxic botulism was allowed to seep in. But before she can tell the town doctor that Mrs. Treadway was murdered, the doctor joins the widow in untimely death. To investigate, the Royal Canadian Mounted Police sends Madoc Rhys, a Mountie who doesn't look the part. Masquerading as a relative, this squat Welshman helps Janet dig into the town's dark side. And what they find is a deadly secret that proves even more poisonous than botulism.