Goodreads asked Tony McMahon:

Where did you get the idea for your most recent book?

Tony McMahon Quest for the True Cross, my first Templar novel, was born out of an abortive project to write a Dan Brown-esque fantasy set in the present day - but with heavy historical references - called The Apostle's Secret. My ex-book agent (we split up over this!) hated it deeply but liked one chapter where I spirited the reader back to the 12th century. He begged me to write a book that was set entirely in that period and - hey presto! - here is Quest for the True Cross.

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