“Cambridge, Michaelmas term, October. The wind bit, the sun hid, and on the first day of class, when she ought to have been lecturing undergraduates about the dangers of using their Cartesian severance spell to revise without pee breaks, Alice Law set out to rescue her advisor’s soul from the Eight Courts of Hell.”
–from Katabasis by R. F. Kuang
Okay, this one is a bit of a cheat, since technically it’s two lines, but the first line is just setting the location, so as far as I’m concerned, it doesn’t count. The second line?… wow, that’s a drop-kick into the story with no safety net. It not only sets up the plot, but it injects a bit of humor on top of it. This tells me that the book will be involved, but probably contain some sly humor for readers to enjoy.