The 6th Extinction is book 10 in the Sigma series and you don't need to have read the previous books in the series to enjoy this book. Although it wouldn't hurt to read them in the right order. Mostly because the series is good and it's interesting to follow the character lives throughout the books.
This book starts with the destruction of a remote military research station that not only kills every single scientist in the facility, but also every living thing within fifty square miles. Animals, plants, and yes even bacteria are killed and the infestation is spreading. Now this must find a way to stop it all.
This book takes us both to the jungles of South America and the icy world of Antarctica as the agents of Sigma has to find a way to stop the spreading that kills everything in its way.
The book is split into two parts; Commander Gray Pierce and others travelers to Antarctica looking for the answers below the ice and Painter Crowe and his group is going after the scientist that created the scourge and who was kidnapped when the military research station was destroyed. I preferred the Antarctic part of the book, it was most interesting with the lost world under the ice and also the one that felt most adventurous.
Meanwhile, Crowe and his team are trying to find the scientist that was kidnapped by the evil man that wanted to destroy the world that we know. The problem for me with the storyline was that It just got to scientific sometimes, too much scientific babble that dragged the story a bit. It was fundamentally interesting the idea that something could be so devastation dangerous that it could kill everything alive, but it just sometimes felt like the scientific babble just went on and on. That could really be why I just preferred what was going on with Pierce and the others because they had to fight for their lives constantly in Antarctica and the world below was so fantastic and dangerous. Yes, there was danger in Brazil, but I just felt less interested in the storyline.
I liked the book, I think it is well-written and fascinating to read. Yes, sometimes the science went above my head, but that only makes me more impressed because it does make the book feel very well researched. Although it did now and then go on a bit too long for my taste. But still, in essence, a really good book.