It is a fictionalised account of Irish giant Charles Byrne (O'Brien) and Scottish surgeon John Hunter.

O'Brien is portrayed as a teller of folk tales and as a poet who aims to save enough money to rebuild the ruined Mulroney's Tavern where as a youth he learned to be a storyteller.

In contrast, John Hunter is obsessed with science; with an insatiable desire to experiment on both the living and the dead, both man and animals; employing body-snatchers to supply his needs.

In the postscript to the 2010 paperback edition of the novel Mantel writes 'In a way I feel, more than with any other book, that I have absolutely no responsibility for what I put on the page'.

She explains that she had initially planned to write 'a big, realistic historical novel about John Hunter, the great surgeon, collector and experimentalist', but as she began to write she had a sudden revelation that she herself was Irish, 'Somehow the giant's story became part of this awakening and the feeling grew in me that in order to find myself I had to go back and capture that voice, that Irishness.