Who was murderer in sparkling cyanide by Agatha Christie?

The murderer in Agatha Christie's "Sparkling Cyanide" is Lucille Duveen.

She is the main suspect throughout the story, and her motive is driven by jealousy and a desire to get rid of her husband's mistress. The evidence, including a mysterious "sparkling cyanide" and a series of events leading up to the poisoning, points to Lucille as the culprit.