A Woman's Vengeance [1948]

Country squire Henry Maurier is patient with his wife Emily, a neurotic invalid, but her brother surprises Henry with his young mistress Doris. The same night, Emily dies of her chronic heart disease, and Henry promptly marries Doris, to the chagrin of neighbor Janet Spence, who loves him. When a post-mortem shows that Emily's death was precipitated by arsenic, Henry is placed on trial for his life. But is he guilty?