Sparkling Cyanide

At her birthday party, Rosemary Barton imbibes a celebratory glass of sparkling champagne and promptly keels over dead — of cyanide poisoning. The coroner's verdict is death by suicide. But was it really? Despite the coroner's conclusion, Rosemary's husband, George, receives anonymous letters informing him that his wife's death was a case of murder. In an effort to trap the perpetrator, George calls the original party together on the anniversary of Rosemary's death.