Based on the best-selling Victorian-set novel by Michel Faber. The first episode of this drama follows William Rackham, a man tormented by debt and an unstable wife, who finds solace when he seeks out renowned young prostitute, Sugar. As he falls under her spell, his life begins to be transformed - but will Sugar be able to withhold her secret desire for revenge on the men who have wronged her?

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.