The book begins quite soon after the events of The Final Empire. Kelsier and the Lord Ruler are dead, and Elend has become king. However, he, his allies and Luthadel (the capital of what was the Final Empire) is surrounded by enemy armies and they lack the manpower, the food and the money to save themselves.
Along with Elend, Vin, his lady friend and general hard case, is the main focus of the book. She struggles to cope as various aspects of her life (loving Elend, trying to protect the city, prowling the nights as a Mistborn) pull her in different directions.
In addition to the armies surrounding the city Elend has to handle political shenanigans and there are a number of interesting, and surprising, twists and turns regarding the city's leadership.
The secondary characters are better fleshed out, I think, than in the first book. The presence of little snippets of lore from the past at the start of each chapter remains, which I really like.
The major characters develop convincingly throughout the story in response to the rising political pressures and possible open warfare, and tension between what's best for individuals and what's best for the city/empire as a whole.
It's a longer book than the average, and personally I quite like that. Sometimes the pace could perhaps be a little quicker, but it never felt like the story was seriously dragging.
I've already bought the next book, so a review of that (and Vanished Kingdoms) should be forthcoming in the days and weeks ahead.