Deep in the grounds of Welland House lies an ancient memorial tower, surrounded by a prehistoric wilderness that isolates it from the rest of the land. When one day Viviette Constantine, the wife of the estate's owner, investigates the tower, she there discovers Swithin St Cleeve, a young astronomer who introduces her to the majesty and wonders of the night sky. Instantly drawn to Swithin, and with her husband abroad, Viviette offers him use of the tower and becomes a kind of apprentice to him, and then, eventually, a lover. Guarded by the tower's safe seclusion, the two star-crossed lovers 'sweep the heavens' and create their own private world, away from the judgement of society... Will they keep their secret, and escape the forces set to drive them apart?