The Enid Blyton Secret Series - Season 3

Prince Paul, still attending the same boarding school as Jack and Mike, invites his four friends to his palace in Baronia for the holidays; but it is so hot there in the roasting summer that the entire royal household adjourns to their castle up in the mountains. Bands of robbers are marauding the countryside, terrorising the local people with their savagery, and Paul is incensed, and determined to find the robbers and have them detained – and, together with his friends, sets out to do this.