[DMcCunney]

Originally Posted by radius

Andre Norton's time agent books are excellent, and you can get a free taste from the Baen Free Library, which is even better. I have no idea about their historical accuracy but they are fun reads (and influential).

Baen has _The Time Traders_ packaged with _Galactic Derelict_ in the Free Library, here.

The other two books in the series, _The Defiant Agents_ and _Key out of time_ are available at Manybooks, here.

If you like the alternative history aspect, Harry Turtledove has written a whole bunch, but the only one which sticks with me is Agent of Byzantium, and that is really more of an adventure/intrigue tale.

Another one to look at is Harry's "World War: In the Balance" series. It's the middle of World War II, and Earth is invaded by aliens. The aliens don't have FTL, and got here travelling centuries in normal space. They chose to conquer Earth next based on data sent back by robotic probes during a period when the knight in armor was the height of military development. They come from a static culture that changes with glacial slowness, and are unpleasantly surprised to find a species with technology only a bit behind their own. Bitter enemies on Earth must find a way to make common cause against the new entrants to the conflict.

H. Beam Piper wrote a series of stories about Lord Kalvan of Otherwhen about a police officer who is dropped in a roughly medieval society. I'm pretty sure that the magazine versions of these are available in Project Gutenberg and similar sources.

Not those, alas. The Lord Kalvan stories are part of a set he wrote about the Paratime Police. The thesis is that First Level society was running out of resources, and working on FTL travel and time travel as a way to get more. A by-product of the research was paratemporal travel -- an means of travelling to the same time in an alternate time stream where things happened differently than in First Level history. An immense paratemporal trade operation resulted, and with it, a police force. The Paratime Police have two missions: to enforce the law on paratemporal traders, and more important, to protect the Paratime secret, and keep people on other timelines unaware that the First Level folks exist among them.

The Lord Kalvan stories concern Calvin Morrison, a Pennsylvania State Trooper who is picked up by accident by a paratemporal conveyer and dropped in the Princedom of Hostigos on the Fourth Level Aryan-Transpacific timeline. On that timeline, the Aryan migration went the other way, across the Bering Strait and into North America. The east coast of America is a patchwork of feuding princedoms with a roughly 16th century level of technology.

Hostigos has a problem. It's facing a war with the neighboring Princedoms of Nostor, Beshta, and Sask, fomented by the church of the god Styphon, whose demands Hostigos has refused. Gunpowder is a monopoly of Styphon's House, and only Styphon's priests know how to make it. Hostigos faces numerically superior enemies, and has little gunpowder to fight them. Calvin Morrison knows how to make gunpowder, and is a student of military history. Senior Paratime Police office Verkan Vall must enter Hostigos, disguised as a Free Trader, and possibly kill Calvin to protect the Paratime secret

Gutenberg has several of the Paratime stories, but not the Lord Kalvan stuff. Ace had the rights to Piper's work, and inexplicably let the rights to everything save Lord Lalvan lapse. The Piper stories Gutenberg does have are here..
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Dennis