What do the guests learn as they arrive at the house?

The guests learn that their host and hostess have been detained and will not be joining them.

"Nothing, sir. We got orders - by letter again - to prepare the rooms for a houseparty and then yesterday by the afternoon post I got another letter from Mr. Owen. It said he and Mrs. Owen were detained and to do the best we could and it gave the instructions about dinner and coffee and putting on the gramophone record."