This book is an excellent end to the story of Tom and Hester. It would not stand up well by itself, however. It is the fourth (and final) instalment in the "Mortal Engines" series, and the last two books seem almost to be one story split into two. To that end, there is a lot happening here that would not make sense to someone picking up the Mortal Engines series for the first time here. 
 The style, quality and feel of the novel is much the same the previous books in the series, so, if you are reading this, you should know what to expect on that front. If not, go read the others first! 
 Seriously. Go. 
 A Darkling Plain picks up shortly after where we left off at the end of Infernal Devices. The story aims, and succeeds in giving closure to all the characters we've followed to this point, with the exception of the Anchorage folk, whose stories ended in the previous book. 
 The plight of Tom and Wren, Hester and Shrike, Fishcake and the Stalker Fang, Theo and Pennyroyal are all settled before the final page. There are some tense moments and some tender moments. 
 I hesitate to name my main gripe, because I fear the root of the problem began in the previous book, saddling this one with the resolving it, but it does feel at times as though the writer wants the reader to be more invested in young couple of Theo and Wren, rather than the older Tom and Hester. Scenes with Tom and Hester in this book sometimes feel reluctant. This may be my own prejudice, however. Having read the all the books to this point, I am more interested in Tom and Hester, who have been in the series from the beginning, than I am in Theo and Wren, who joined us in book three. 
 Reading this story requires you to ignore some of the niggling "well that's impossible" feelings that certain events spark, but, if you can accept a fictional world in which cities roam the Earth on giant wheels, then there is nothing in this book that should be beyond your acceptance. 
 The ending, after all the individual story arcs have reached their climax, is one that I felt particularly poignant, especially when you consider the world that the books are set in. 
 To sum up, if you haven't read the previous books in the series, this book would not be a good read for you. Start with Mortal Engines, and I have a feeling you'll be here soon enough. If you have read the other books, you were probably going to read this one anyway. I'm here to tell you; it doesn't disappoint.