Definitely watch the three parts of this story in order.
There was no way I was going to stop watching this trilogy until I found out "who dunnit." I found the ending to have left a few loose ends and be a bit of a let-down, but it works. One of Hitchcock's favorite actors, John Williams as the amusingly annoyed and baffled Inspector, is a blast to watch as he sorts out too much evidence and too many suspects.
Robert Stevens directs the teleplay by Francis Cockrell, based on Alec Coppel's inventive story.
With John Williams, Rosemary Harris, Alan Napier ("Excuse me, sir--it's the Bat-phone"), Charles Cooper, Melville Cooper, Charles Davis, Anthony Dawson, A.E. Gould-Porter, Nora Marlowe, and Peter Gordon.