I have seen all of the old Hercule Poirot with Peter Ustinov and I liked most of them, and I had to watch this one too as it's considered the weakest of those movies. It wasn't terrible tho.
This film is set in Jerusalem. When it begins the Boynton family (with Piper Laurie as the martiarch Emily and Carrie Fisher as one of her daughters) is preparing for destroying the patriarch's will as he died recently. They go in Jerusalem and Poirot casually happens to be there. Along them also Lady Westholme (Lauren Bacall), her secretary Miss Quinton (Hayley Mills) and her lawyer Cope (STARSKY & HUTCH's David Soul). At a dig, Emily is found dead with pin marks on her wrist, suggesting that she had an injection with a syringe. With the help of Colonel Cadbury (John Gielgud) Poirot investigates. I won't spoil the ending.
The scenery is great and the soundtrack was decent. The cast is full of famous stars apart Ustinov: Lauren Bacall, Carrie Fisher, Piper Laurie, David Soul and legendary stage actor John Gielgud are quite an ensemble cast of A-listers. The problems with this movie were that at times it was sloppy and slow paced, and Mrs Boyinton looked a bit too cantankerous than a tyrant. And the plot twist at the end was hard to believe.
Not a complete disaster but with some faults (and the fact that it was produced by Cannon films probably says a lot).