Agatha Christie 
Blue Geranium [PDF ebook] 

George Pritchard, whose wife is a semi-invalid dreadful woman, ends up firing all the nurses for her bad temper. Mrs. Pritchard has a weakness for fortune tellers, one afternoon she receives Zarida, who announces all kinds of dangers related to blue flowers and predicts that a blue geranium will be the foretaste of her death. The walls of her room are wallpapered with various flower patterns, but none of them are blue. However, for some strange reason, some of the flowers turn blue. After the woman’s death from heart failure, all suspicions point to her husband. Did it scare her to the point of death? Was it George or is someone else involved?