Jacob and Fox may not have found Jacob's brother Will, but they have found something even more unexpected in the Mirrorworld: happiness. Just as they give up the search to enjoy their new life together, Will appears.

But now Jacob isn't sure he can trust his own brother. Travelling with Jacob and Fox's deadly enemies, Will is on his way to Nihon, beautiful land of sea serpents and samurai, talking forests and magnificent foxes, in pursuit of another magical Mirror. The pair can only follow.

If they are fortunate, what they find could save them. If they are not, they will find painful truths, terrible risks and a greater danger than they could ever have imagined.