Matthias Fitzosbert, illegitimate son of a parish priest, has a unique relationship with Rosifer, the fallen angel—the spirit he loves yet hates, strives to placate yet ultimately must flee. The story of Matthias is played out against the vivid panorama of the Middle Ages—the fall of Constantinople; the last throes of the Wars of the Roses; the terror of witchcraft; the loneliness of the Scottish marches; the battlefields of Spain; and finally, the lush jungles of the Caribbean, where the Rose Demon and Matthias meet for a final deadly confrontation.