At the end of the previous book, the author killed Maxwell then resurrected her (literally) in an alternate universe that was similar to but different from the one in the first three books. This novel picks up where book #3 left off, and moves the story along.
I don't like it when authors reboot a series like this. They throw away the large volume of stuff they've established by creating a new world.
In this alternate dimension, her lover Leon Farrell is still alive. Also, we have the Time Police who prevent people from breaking the rules in regards to time travel, and they are after Leon, causing the two of them to be on the run for quite a while. Most of the people at St. Mary's don't trust her, because her alternate self died here, and they don't know who or what she is.
The writing and the story are good, as usual. But I really dislike the reboot, thus 3/5 stars.