You can always count on Poul Anderson for a good time travel story, and The Corridors of Time is no exception.
In the 40th Century, the world is dividing into two camps - The Wardens, who control the Eastern Hemisphere, and the Rangers, who control Western. To Malcolm Lockridge, an ex-marine college student of the 20th century, the distinction between Good and Evil is an easy one to determine after he recruited by Storm Daraway, one of the leaders of the Wardens.
Storm, using the cover story of hiring Lockridge to help recover some long lost Ukrainian Freedom Fighter gold buried in the Jutland, steals him away to Neolithic Denmark and fills him in on the war between the Wardens and the Rangers that is being waged across all of time. She brings Lockridge in on her side - and as her lover - and that choice is an easy one for Malcolm after Brann, the ruler of the Rangers, leads a hoard of Indo-European barbarians against the peaceful village that is hosting them in an attempt to capture Storm - which he does and then proceeds to torture her for information.
Lockridge, decides to escape and seek help. He makes his way through the local Time Corridor to Reformation Europe in search of a contact that Storm said would be waiting each All Hallow's Eve at an inn in Viborg. This contact will lead him to her cohorts who will mount a daring rescue attempt using English warriors from the 16th century.
But, Malcolm must determine if he has chosen the right side in this war... or even if there is a right side; and through it all he will learn his pivotal role in the future that follows the 40th Century.
A Guide to my Book Rating System:
1 star = The wood pulp would have been better utilized as toilet paper.
2 stars = Don't bother, clean your bathroom instead.
3 stars = Wasn't a waste of time, but it was time wasted.
4 stars = Good book, but not life altering.
5 stars = This book changed my world in at least some small way.