After the Marsupilami causes a series of disasters, Spirou and Fantasio finally resolve to bring the strange animal back to its birth place, Palombia. Unfortunately, it's a nation in turmoil, as they quickly find upon their arrival. The military is all-powerful, rumours of impending war are growing and a ruthless tyrant has seized power. To counter the dictator's plans, the two adventurers' only weapon is the Count of Champignac's latest outrageous invention: a mushroom extract that makes metals go soft.