The story is set in British fortress and colony Gibraltar. A man, a Spaniard named Gil Braltar, dresses up as a monkey and becomes leader of a group of monkeys living there (Barbary macaques). He incites attack on the fortress. The attack, initially successful, is foiled by a British general. This general is so ugly that the monkeys believe he was one of them and obey him when he leads them out. Verne's conclusion is that in the future only the ugliest generals will be sent to Gibraltar to keep the colony in British hands.