The Rule of Four

Ian Caldwell is an American novelist who co-authored the 2004 novel The Rule of Four. His second book, The Fifth Gospel, was published in 2015. He was born in Virginia where he met his future writing collaborator, Dustin Thomason. Caldwell was a Phi Beta Kappa at Princeton University where he graduated in 1998 with a degree in history. After college, while working with Thomason on their first novel, Caldwell worked at MicroStrategy in Tyson Corner and taught test preparation for Kaplan.

After graduating from their respective colleges, Caldwell began working with Thomason on the novel The Rule of Four. After writing together for a summer, the two continued to collaborate online for the next five years. The plot centers on four Princeton seniors attempting to solve a mystery related to the Hypnerotomachia Poliphili, an Italian work from the early Renaissance. The book was published by Dial Press in 2004, spent 49 weeks on The New York Times Best Seller list.

It took Caldwell ten years to complete his second work, The Fifth Gospel, which was published by Simon and Schuster in 2015. This solo work tells the fictional story of two brothers, both priests, exploring the Diatessaron, the "fifth" gospel, and how it might lead to reconciliation between the Roman Catholic and Eastern Orthodox churches.

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