For the fourth book in the series we take a break from the main narrative of the proceeding three, and follow events from the perspective of some new characters, most notably Nilda and her teenage son Joe.
Through them we live through the early days of the outbreak, learning as they do, what is happening, as they go out and about, which Bill couldn't do with his broken leg, and without the background information that Bill had from his connections.
This gives an entirely new view of the world as first switch between going it alone, then grouping up, and then going alone again. Along the way they meet all types of other survivors from the good to the downright bad, and quite a lot of zombies, all of whom are bad.
There are some nice crossovers between this new strand and the original strand, in both minor and major ways, although you probably won't need to have read the first three books to follow this one.
However, as with those this is a great, exciting read, with many changes of setting as the characters move around the country, knowing that no one is safe.
The only question I would have is why this, and the fifth book, aren't included on the Surviving The Evacuation series page, as many people visiting that page may not realise there are more books to read, and that would be a great shame.