Sidony Redruth is a young English woman who, after fraudulently winning a writing competition, is sent by her editor to write the first-ever travel book on Hy Brasil, a near mythical island somewhere in the Atlantic whose very existence has been a matter of debate as late as the nineteenth century.

Elphinstone's plot takes the island location as its starting point, throws in some old-fashioned piracy, a lost treasure, modern-day drug smuggling, political intrigue, an active volcano and a tragic love affair. Told through Sidony's notes for her book, Hy Brasil is a compelling and magical adventure story.