Time Traders II: The Defiant Agents & Key Out of Time

Time Traders II: The Defiant Agents & Key Out of Time - Andre Norton I love the first book "The Defiant Agents" but not so much the second one. For some reason "Key Out of Time" is slower paced and has to do with Time Travel that just does not seem plausible to me. I love most Time Travel and dimensions I read, but this one for some reason just seems unbelievable.I enjoyed the first three books in this series, but the last three books just got boring.