The book is rather strangely constructed, no influence from Piper. Clearly the first section, the non-Kalvan stories, was originally printed alone. Then the Kalvan novellas were printed alone. So this book has an Introduction that has only the first set in the table of content and a single line addition that the second set was added to the first set.
The Introduction is by John F. Carr and I found it to be stilted and rather patronizing. I enjoyed the info about Piper, but most of the info he included about the stories came word-for-word from the stories.
All of the book is about Paratime -- a set of timelines where only one group of people can move between them. The Paratime Police have to take care of a lot of problems in the first set.
In the Lord Kalvan stories, the Paratime Police are only in small places. Kalvan is actually a near-our-time sheriff who gets caught in the method of changing timelines and dropped in someplace that he didn't know, but was smart enough to manage to fit in, and to help the people he meets (primarily because of the history he learned in school).
These stories were written long ago and everybody smokes something all the time and the adults are "men" and "girls." They were interesting stories, but I did feel a bit like I was looking back in time.