Fantasy Trilogy; shifting castle

[I Eat Robots]

Hello, I'm trying to recall the title/author of a fantasy trilogy I read about eight years ago.
The setup was a soldier being called back to duty, to lead troops to a place where he had lost all his men against what turns out to be a powerful young girl (named Night?). I think over the course of the series he loves and tries to protect her. There is also a castle that changes shape. The second or third book featured a city where lower caste orphans were forced to live on the rooftops and nets above the city, only stepping down to the ground once a day. Thanks!

[hammerhead]

was it the series of books called dungeons i believe or something similer to that, can't remember the author thou