Seduced by her charms, William moves Sugar out of Mrs Castaway's brothel and into a flat of her own in Marylebone. Finally independent, Sugar becomes a fixture in William's life and secretly continues her role as guardian angel to his volatile wife Agnes. But as their relationship intensifies, will Sugar take things too far?

Sugar is thrilled at the prospect of moving in to William's house as governess to his neglected daughter Sophie. But she soon finds Agnes' condition to have deteriorated, worn down by the constant visits from Dr Curlew, and Sugar makes a promise to help her before it is too late.

As Sugar's bond with Sophie grows stronger, her relationship with William becomes more troubled. When her stay in the Rackham house becomes a risk, Sugar is forced to make a life-changing decision for her and for Sophie, with major consequences for all involved.