Allamanda — Michael Williams

From Kirkus Review:
The fantasy saga of the Hawken family continues, ten years after the events of Arcady (1996). Drunken old Endymion skulks in the huge, rambling, decaying house, Arcady, until his son Garrick discovers an Absence - a terrifying, wandering, formless, all- consuming blob of space - beneath it. So the Hawkens must abandon Arcady and head for their last estate, Allamanda, presently occupied by Allegra and family - who are none too pleased to see the refugees. Along the way they've picked up Solomon, who, despite a tarring and feathering, remains convinced that his version of the holy writ, the New Text, will defeat the Absences. While Allegra schemes over the fate of Allamanda and recruits her son Miles as a spy, Garrick shows an interest in Miles's sister Flora. But the girl becomes trapped inside an Absence. So Garrick, troubled by dreamlike blackouts, must brave the Absence and its horrid inhabitants - filthy, ragged, feral children known as Blights - to rescue her.