The Gate Thief, picks up just after the first book The Lost Gate ends. There we met Danny North, a teenager who had just come to understand that he was a gatemage, a wizard with incredible abilities. After untold generations of wars and dispute, a fragile truce has existed among the different mage clans on Earth based on exposing and killing any mages with the ability to open portals that connect two different places. The practice of culling the gatemages was felt necessary because they might have the ability to open a gate between Earth and the distant world of Westil. If a mage were to make the trip from Earth to Westil and back again, his powers would be immediately enhanced ten-fold. Such wizards would then give their clans an advantage that might allow them to rise up and seize power.
Danny has slowly grown into his strength over the several years since he first discovered who he was. He has already survived an encounter with Loki after he made his first Great Gate to Westil. Loki is a powerful gatemage who closed up all gates between Earth and Westil more than a millenium ago. Furthermore, he had the ability to steal all of the gates created by any gatemage. After Danny encountered Loki in Westil, he rendered Loki nearly impotent, somehow using the fragments of what he knew, along with his great power, to take nearly all of Loki's gates. However, instead of becoming drunk in his power and raising himself to be a god on Earth, he struggled to understand why Loki had closed all of the gates in the first place. Loki was no prankster as had been assumed. Instead, he had taken on the burden and the responsibility to protect both Earth and Westil from Set and his minions, powerful creatures who sole purpose was to enslave all of humanity.
The Lost Gate was a decent story, although I felt that the character development was a bit lacking. More specifically, I felt no particular reason to embrace Danny North. However, the settings that Card had developed, as well as the ideas in the narrative, intrigued me and made me want to push on to The Gate Thief. It turns out that I was well rewarded with the second part of the story. It was tightly written, compelling, and had some good lessons to teach. In the afterward, Card mentioned that he is presently planning for his Mither Mages series to be completed with a third volume, although a release date is not yet set.