Hercule Poirot is invited by a friend, the famous actor Sir Charles Cartwright to a dinner party. At the party, while drinking cocktails, one of the guests, Reverend Babbington, collapses and dies. Sir Charles says to Poirot that he thinks he was poisoned but the contents of his glass are free of anything toxic, and the event is put down to natural causes. Even Poirot does not suspect foul play. Then a month later, Sir Bartholemew Strange, a friend of Sir Charles, dies during a dinner party. This time it is clear that he was murdered - poisoned. Poirot suspects that the two deaths are linked and revisits his conclusion that the death of Reverend Babbington was due to natural causes. Sir Bartholomew's butler, Ellis, is the prime suspect but he has fled and is nowhere to be found. Poirot doesn't believe that the case is that simple.
Quite intriguing, and one of the better later-season Poirots. The later seasons suffer from the lack of Hastings, Japp and/or Lemon as they gave a warmer, more engaging feel to the stories. Without them the stories feel a bit cold and matter-of-fact.
However, here we have Sir Charles Cartwright, ably played by Martin Shaw, who wants to test his sleuthing abilities, having played so many detectives on stage. Moreover, we have his delightful girlfriend "Egg", played by the gorgeous Kimberley Nixon. Nixon gives the episode a wonderful energy and is utterly mesmerizing.
Ultimate plot is quite credible and not at all far-fetched, unlike many of the Poirot mysteries. The murderer is difficult to spot, but the clues are mostly all there.