On Halloween, Genevißeve invites her students to dress up as prisoners to visit the former Trois-Rivißeres prison. The visit goes well until Dominic finds himself behind bars with the guide. Impossible to get out! The guide forgot his key in his trouser pocket, and to retrieve it, he must contact his grandmother. Once Dominic was freed, a few companions who laughed at him and his fears found the situation so amusing that they locked themselves in the next cell. To make matters worse, the guide forgot the key again, but this time in his shirt pocket which is at the cleaners...