The Summer of the Mourning Cloak is the story of a visit which changes lives forever. The title refers to a beautiful, rarely seen butterfly, The Camberwell Beauty, sometimes know as The Mourning Cloak, which is used throughout the novel to symbolise the emotional journey of the protagonist. The main character is an 11-year-old girl, Hyslop, who arrives in England from Italy with her emotionally distant mother Vanessa. In the past they have flitted from the shelter of one wealthy man to another, but Hyslop finally finds love and stability from her godmother Sandy and an eccentric old man, Sir Northcote Hemmings. He teaches her about butterflies and asks her to find him a Camberwell Beauty, a butterfly that is something of a Holy Grail for our protagonists.

The parallel world of butterflies that is explored throughout the narrative invites the reader into Hyslop's imagination, where her fascination with butterflies mirrors her desire to be free from her mother's cruel domination. Hyslop is shadowed by a lonely local boy, Zak, who is bullied both at home and at school, and his fascination with her reflects the way her glamorous mother charms everyone with her beauty. As flighty Vanessa's powers start waning, Hyslop is just beginning to find her wings. Will Hyslop find her ideal habitat in the end?