Which is one of the best Christmas books, ever.
It's about the Herdmans, a family of absolutely terrible, trouble-making kids. The narrator's younger brother Charlie accidentally gets them to attend a service once, where the announcement is made about the pageant. (The narrator's mother is running it, the usual woman having broken her leg and being in the hospital.) So they show up and volunteer to take all the roles, much to everyone's horror. And then the narrator's mother has to read them the Christmas story, because they had never heard it before.
Despite which, they take all the major roles. Leading to adventures in rehearsal and then onward to the pageant itself.