A Tale Of Time City by Diana Wynne Jones

The time is 1939 and the location is London, England.  Vivian Smith is one of the many children who are being moved out of London into the countryside in order to escape the nightly bombings that are occurring.  In Vivian's case, she is on the train along with lots of other children, her destination a cousin of her mother's who has grudgingly agreed to take her in for a while.

But Vivian doesn't get there.  She is time traveled to a location far in the future by two boys around her age, Jonathan and Sam.  They live in Time City and there is trouble there as well.  The area is about to become unstable with consequences for all eras going back into the past.  The boys believe that Vivian holds the keys to fixing the future so that Time City will be saved and the past will remain as it is commonly accepted to be.

Vivian isn't sure that she is up to the task but realizes that it is the only method she can use in order to get back to her own time and back to her parents.  She agrees to help.  The three children start to travel to various time periods, hoping to capture all the caskets that are necessary to save Time City.  They aren't very successful since there are powerful forces working against them.  All appears lost but is it?

This is a young adult book and the story is much simpler than the intertwined texts and plot lines that most science fiction/fantasy readers are used to.  The characters are fairly flat and the explanation of how things work is simple.  This novel is recommended for young adults interested in fantasy reading.