Lenglumé, a wealthy citizien, has arranged a night out with former classmates from his boarding school without his wife's knowledge. The following day, he wakes up in bed with a man. Despite the dreadful hangovers, Lenglumé and Mistingue recognise each other as old pals from school. However, they fail to reconstruct what happened the previous night after the banquet. An article in an old newspaper seems to shed some light on their memories. With increasing horror, they discover they have the circumstantial evidence for a brutal murder of a coal-girl in their very own pockets. On top of that, a witness shows up.