 When spoiled Betty rants against an article in the paper that students nowadays are self-centered without a social conscience, Billy sees his chance to enlist the bunch for a demonstration against pollution in the Dijle, the city s river. Only Charles-Victor declines, explaining the downsides of demonstrations for authorities and participants. Jef and Odilon (who doesn t get is, as usual) only pretend to participate, but eagerly accept to take effective charge of distributing posters over each café, after all not having a drink in each would be rude. The preparations keep going wrong, and on the day itself, rainy weather is far from the worst danger, and there s another surprise...