Second books serve different purposes in different contexts. Books like last week's entry from Christopher Moore allow the author to return to a setting and explore it more fully. An author might use such a book to tie up loose ends from the first book, and also introduce new loose ends that might spawn a third book. At the same time, such a book needs to be sufficiently satisfying on its own that readers don't feel cheated by not having read the first book, nor by not having a third book available.
This week, however, we have the second book in a traditionally constructed trilogy. This sort of second book serves a completely different purpose. Yes, the author IS exploring a setting more fully, and drawing characters more sharply, but she is also advancing her broader plot, introducing new complications for her characters, and generally building a bigger story. It is far less necessary for this sort of book to stand alone, because there is an implicit assumption that the readers have a) read book one of the trilogy and b) intend to continue onto book two. Indeed, the second book in a trilogy must serve as a bridge between books one and two; on some level, were the second book to stand alone, it would have failed in its purpose. At the same time, of course, the book must be narratively complete, with a clear beginning, middle, and end, even if the beginning is anchored to an earlier book and the end strongly points towards a later one.
Siege and Storm is the Leigh Bardugo's second book in her YA Grisha trilogy. (It is also her second published novel, but that's a different discussion.) This trilogy is a Russian inflected fantasy, in which a body of "grisha" engage in what we the readers might deem magic, but they view as science. Through the manipulation of mater at the atomic level, they can perform wonders in a narrow range of areas: human bodies (healers and killers), natural elements (air, water, and fire), and material elements (construction and alchemy). Bardugo has constructed a compelling world around these grisha, who serve as a powerful second army for the nation of Ravka. Ravka's neighbors tend to distrust or actively hate grisha, focusing instead on technology. Thus, there is an element which some might deem "steampunk," but which I think probably does not apply here.
The books tell the story of Alina and Mal. In the first book, Alina discovers that she is a powerful grisha, able to manipulate light. This makes her important to the leader of the grisha, who can manipulate darkness. Ravka is riven by a "sea" of darkness; an accident caused by a previous Darkling, and Alina might be able to destroy or otherwise mitigate this Unsea. Mal is a soldier whom she loves, a skilled tracker, but not magically inclined. There is, consequently, a class divide.
In the first book, Alina discovers that the politics of Ravka are deeply complicated and full of betrayal and danger. The first book ends with Alina and Mal on the run, and that is where we pick them up at the beginning of this book - hiding on the partially explored other continent. From there, Bardugo offers her readers an adventurous tale with pirates, sea monsters, flying craft, crash landings, wild hunts, land monsters, human monsters, more politics, and a civil war. There is betrayal and redemption and excitement all around. It's a very good book.
It's also a very good second book. While it is possible to pick up the basic thread of the story from book one, there is a strong sense that everything - the plot, the character interactions, the politics, the complications of the world - would make better sense after having read book one. Additionally, while there is an ending to THIS book, there is also a clear sense that this is not the end of the STORY. A trilogy works best when all three books are good books by themselves and ALSO good parts of the larger whole. Bardugo accomplishes both goals with this book, and I do recommend the trilogy AND the book to all of you who love YA fantasy filled with darkness, betrayal, regret, and blood.