Many of you will be familiar with the late H. Beam Piper's excellent Paratime novel, "Lord Kalvan of Otherwhen". In it, Calvin Morrison, a Pennsylvania State Trooper, is swept up into an alternate timeline with roughly 30 years war era technology, and dominated by the power of Styphon's House The priests of Styphon discovered the recipe for gunpowder, and keep its production a monopoly that they uses to enrich themselves and manipulate the affairs of a huge swath of territory in a very different version of North America.
John F. Carr has written a number of sequels to the original book, this one being the 6th, and co-authored by Wolfgang Diehr. The latest offering concerns a sideshow operation of fifth column activities taking place in the Great Kingdom of Hos-Bletha. Although the now Great King of Hos-Hostigos, Lord Kalvan, barely appears in this novel, IMHO in many ways it is the truest in overall feel to Piper's original.
A brief review can be found on my blpg at:
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This newest sequel was delayed a year by a severe illness on the part of Mr. Carr, and was only released in November 2014. It is presently only available in a top quality but expensive hardcover version, but all of the other sequels are now available in much more economical e-pub and kindle formats. Links for purchase of all of John's novels are included in the blog post.
There are several other Kalvan related posts on my blog over the years, including this one about the other 5 sequels:
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and others found by clicking on the Lord Kalvan tag on the blog.
Down Styphon!
Peter