If you pick up this book based on the title you'd be disappointed. It carries on the story set-up in [b:The Long Earth|13147230|The Long Earth|Terry Pratchett|https://d202m5krfqbpi5.cloudfront.net/books/1335532694s/13147230.jpg|18164154] but set 10 years later.
Many worlds have now been populated by humans, who use trolls for free labour, and the trolls don't seem to mind, of course if they did they could just step (teleport to another duplicate earth) away. Unfortunately for humanity's expansion of the long earth, the trolls are beginning to drop tools and escape after some bad treatment of trolls by a few unethical humans. The trolls are able to communicate across the long earth by the "long call" a song that can spread news and information surprisingly quickly. What the book didn't show was the alleged humans who were missing the trolls, or demanding their return or asking for help for their return. The main protagonists' regularly said how important the trolls were for the ecology of every long earth they had been established in, which makes sense as they hunt and gather and thus would have shaped the evolution of any animals and plants they ate, or competed with. This troll migration leads to a "war" between the colonists of the long earth, original earth's military who travel in Air balloons across the earth's.
I wasn't that invested in what happened, and the climax was so anti-climatic to be laughable. I did enjoy the fact New Zealand had a significant part towards the end of the book, but I did see it coming, and if you know any Maori (aboriginal people's of New Zealand) mythology you may guess it too. Overall, it was an okay read and I won't be actively hunting out the sequel, but may read it to be a completest.