When the Marsupilami causes chaos all over town, Spirou and Fantasio decide that it is time to take him back to his home in the Palombian jungles.

After an eventful journey by cruise ship, they find that Fantasio's shady cousin Zantafio has reinvented himself as General Zantas and become the country's ruthless dictator.

The now power-mad Zantafio, intent on invading a neighbouring country, offers them top positions in his army.

The pair decide to feign a change of heart, and plan to foil the invasion using one of The Count of Champignac's curious inventions... Two characters introduced in previous stories return for the first time in this one: the resourceful Seccotine, and the shifty Zantafio who was last seen repenting his scoundrel ways at the conclusion of Spirou et les héritiers, but later evolved into a worse villain.

The sequence where Spirou and Fantasio melt a whole army's gear is an early, still quite gentle, expression of Franquin's anti-militarism, which he would let loose much more ferociously in Gaston Lagaffe and Idées noires.