Children plus tesseracts = adventure.

Other Comments:

A boy and girl travel through space by "wrinkling" time. They meet fascinating creatures and delve into the mysteries of the universe. Clever and captivating. A young adult book adults can love. – Jill Nelson

A subtheme which I found particularly interesting was the portrayal of evil taking the form of uniformity, and good taking the form of diversity. There are lots of examples of works which sound a warning against mindless conformity, but I have never encountered one which framed the conflict between diversity and uniformity in terms of good and evil. (No doubt largely due to the fact that most such works are not, in fact, arguing for freedom or diversity as such, but for "freedom" to throw out moral standards and do "whatever I want.") – Greg Slade

For the print editions, check the book page.