The novel was initially self-published under the title The Highfield Mole: The Circle in the Spiral on 17 March 2005, with a limited run of 500 hardback and 2,000 softback copies,[REF] financed by the sale of Roderick Gordon's house.
The sequel, Deeper, was released in the UK on 5 May 2008 (in the United States on 3 February 2009), and a third book, Freefall, was published in the UK on 18 May 2009 (in the United States on 1 February 2010).