This is not a book for the faint of heart. Although standing independent from Neal Asher’s other books (the Polity series), it shares a few characteristics with them, including graphic (and sometimes gratuitous-feeling) violence. It also has some mind-bending time-travel science, lots and lots of mind games played on the characters and the reader, and (as always with Mr. Asher’s books) excellently detailed biology.

The book mainly follows two characters from the 22nd century, Polly and Tack. They are both pulled into a three-way clash of civilizations against their will. The players in the war across time are two civilizations and one very scary individual, the eponymous Cowl. The civilizations are the Umbrathane and the Heliothane, both based in our distant future.

Cowl has set up shop at the beginning of life on Earth, and is pulling sample people back to him from across time. Thus are Polly and Tack ensnared into the plot. Tack is by far the most compelling character in the book. Starting off as a soulless government assassin, he becomes a pawn in many ways and for many people, only achieving rebirth as his own person through lots of pain and experience.

The characters travel through many times, past and future. In some of the near-past scenes, the author can’t resist the temptation to randomly plunk his characters near to famous historical personages, an impulse that I wish more authors could resist. But that is quickly over, since the vast majority of our past doesn’t contain humans at all. When the characters travel through prehistoric times, into the eras of great mammals, dinosaurs, and beyond, the scenes and scenery are absolutely convincing, a real strength.

Overall the book is an interesting read. It isn’t the most fast paced book, and sometimes it becomes very hard to follow the rules of the game and picture how things should be working. Generally speaking, I found it better to go with the flow, trust the author and the characters, and watch the many battles unfold. Some plot twists are predictable, others aren’t. As time-travel books go, this is certainly one of the best that I have read recently.