In the book, "The Murder of Roger Ackroyd," what major events took place in the book?

The death of Mrs. Ferrars, who overdosed on Veronal, a sleeping medication. Much of the town (including Dr. Sheppard’s gossip-loving sister, Caroline) believes Mrs. Ferrars poisoned her husband a year before. Caroline now speculates that Mrs. Ferrars has committed suicide with Veronal over the guilt.