Let the readers examine the evidence.
Edgar Allan Poe set The Gold-Bug on Sullivan’s Island. If your book group likes puzzles half as much as it likes poking holes in a narrator’s account, put those habits to work. At a private supper I can hand one guest an object to examine and appoint another to report what changes. Neither needs to have finished the book, a feature several members may quietly appreciate.
Choose whether the story is a chapter or the whole evening.
Keep the book discussion first if that’s why everyone is coming. I can set up cards and a short parlor mystery for the group after dessert, then stay at the table for anyone who wants to watch more closely. If you’d like Timothy Starnes & His Many Night Visitors as the main event instead, give it two uninterrupted hours and seat the adults together. It’s theatrical séance entertainment, with no promised correspondence from Mr. Poe.
Before you send the invitations, count the seats around the table, not every chair in the house. Ten to fifteen adults works well for the séance when all can see. Tell me what the group enjoys arguing about and we’ll decide how much evidence to leave them.