Breton late summer in the legendary Arthur forest and eccentric scientists in pursuit of eternal glory. The forest of Brocéliande, with its picturesque lakes and castles, is said to be the last remaining fairy realm - according to the Bretons. Countless legends spanning several millennia are located here, including those of King Arthur and his Round Table. What better place for the long-overdue company outing of Commissioner Dupin and his team during these Breton late summer days? However, the murder of an Arthur researcher throws a wrench in the works for the commissioner. Against his will, Dupin is swiftly appointed as a special investigator in a brutal case that soon claims more victims. What do the assembled scientists know about the recent excavations in the area? What are their views on the plan to transform parts of the forest into an amusement park?.