The guests arrive, get situated, and have a nice dinner. What happens after dinner?
After dinner, the guests find out why they are really there. They were collected because each one is a murderer. After dinner, they hear a voice telling them so! It begins:
Ladies and Gentlemen! Silence please! … You are charged with the following indictments: (p. 38)
They are startled by the voice and look around to see who it is. The recording explains which murder each one committed. It naturally is very eerie. At the end, the recording refers to the guests as prisoners and asks them if they have anything to say in their defense.
Until they hear the recording, they do not realize that they have all been accused of murder. Naturally this causes a commotion. It turns out that they are not able to leave the island, because the supply boat is not coming back. The plot thickens!