A group demanding the independence of Cornwall has committed several attacks in Britain. Captain Blake, tasked with securing the site of an official visit by Prince Charles in Cornwall, must contend with the locals'' sympathies towards the secessionists and their leader, a mysterious High Druid. Meanwhile, Professor Mortimer is about to test his latest invention, a revolutionary excavator - in Cornwall. And as for Olrik, his new cellmates have a pronounced... Cornish accent!