Darion, Lord Rivers, Undersecretary to the Foreign Minister of Calaria, has a problem – his wife wants him to promote her brother Gregorius Bass, whom Rivers considers a hopeless fool. Fortunately, an envoy's post has just fallen vacant in the conveniently distant and unimportant city of Bonvidaeo. We learn from Bass's journal of the odd customs of the city, where masks must be worn at all times.