This is book 9 of the "Young Wizards" series.

This note contains spoilers for the book.

Most recent book in this series, at least as of when I read it.

Mars is strange. There's no planetary kernel, and there's a weird relationship to it throughout human history. Kit is very interested in the place, and is an expert on the literature as well as the science we've got.

Some early investigations show artifacts left behind. They're very strange artifacts, operating on bizarre magical levels.

We end up meeting and dealing with the people who destroyed the fifth planet to make the asteroid belt, who have been holed up on Mars in stasis for a long time. Their wizardries communicate with us using our views of Mars—which leaves Kit dealing with meeting Dejah Thoris, close enough. This emphasizes some strains that have been ongoing between Kit and Neeta for a while now, and seems to somewhat resolve them.

We also, once again, save Earth. The people in statis on Mars had plans for it, but they get thwarted.