The Defiant Agents

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The Defiant Agents is the third novel in The Time Traders series by Andre Norton. It was first published in 1962, and as of 2012, had been reprinted in ten editions with cover changes, as well as twice in a combined edition with Key Out of Time. It is part of Norton's Forerunner universe.
The Defiant Agents continues the series’ premise, an encounter between Western heroes, and the Russian Communists, and a mysterious alien race that has used time travel to alter Earth. Most interaction in this novel is in an American Indian-like setting.
Kirkus Reviews comments, “Andre Norton, a polished writer of science fiction, weaves [her] outlandish fare in patterns intricate enough to attract the most devoted addict. Do not try to contrive a consistent political allegory out of [her] flight into fantasy. This is pure science fiction....”