Lady Constantine breaks all the rules of social decorum when she falls in love with the beautiful youth Swithin St Cleeve, her social inferior and ten years her junior. The tower in question is a monument converted into an astronomical observatory where together the lovers 'sweep the heavens'.

Science and romance are destined to collide, however, as work, ambition and the pressures of the outside world intrude upon the pair. In what Sally Shuttleworth calls 'a drama of oppositions and conflicts', Hardy's story sets male desire against female constancy, and 'describes an arc across the horizon of late nineteenth-century social and cultural concerns: sexuality, class, history, science and religion'.