Come whether or not you finished it, and say so
The book
About three hundred pages, chosen by whoever hosted last month. Copies are in the shop at a discount and in the library.
Not finishing
Entirely normal and worth saying at the start. Spoilers are then flagged, which everybody appreciates including the people who did finish.
The evening
Two hours in the back room, about twelve people. One drink and a great deal of digression.
