On the zany night Thurber describes, the following people are in the house: James, the narrator; his mother; his father; James's brothers, Herman and Roy'; and Briggs Beall, who is the boys' first cousin. The bulldog, Rex, is also at home with them. We learn of other characters, such as the grandfather and some assorted aunts, but they are not in the house during the night in question.
As the story unfolds, a chain reaction of events begins when the father decides to sleep in the attic so he can think. When the mother thinks his attic bed has collapsed on him, she screams, and this sets the entire household into an uproar in the middle of the night.