The City Book Trilogy

The City Trilogy was written for adult readers under the pen-name Darren O'Shaughnessey originally, before the pen-name Darren Shan was used for his children's books. The third book was originally never published, and the books went out of print until 2008. They were published by Orion Publishing Group.

The first, renamed Procession of the Dead, was re-released in March 2008, and the other two followed in March 2009 and March 2010 respectively. The first two were originally released under the pen-name of D.B. Shan but were subsequently re-issued along with the third book under the name of Darren Shan.

The story of The City Book Trilogy revolves around an unnamed city ruled by gangsters and a group of ancient Incan Priests who wield the magical power of 'the Ayuamarcans'. The stories of the first two books run parallel to each other, while the third book takes place ten years after the first two.

Procession of the Dead (Formerly 'Ayuamarca') - First published in the United Kingdom in February 1999 and then in Russia. Re-released in March 2008 under the 'Procession of the Dead' title.

Hell's Horizon - Sequel to the first book. First published in the United Kingdom in February 2000. Republished March 2009.

City of the Snakes - First published March 2010. The story of the third book takes place 10 years after the first two books.

http://www.darrenshan.com/books/

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Wikipedia