Follow-up is a bitch. That's an easy way of seeing the paradox at the heart of a long and successful writing career. At best, an author brings a new vision, a new style to the readers with each and every work. The specific elements that comprise that vision and style are certainly important to the appeal of the writing, but the ineffable newness of the combination is often the key. The paradox an author must unravel is how to present a set of familiar elements -- that readers enjoy and look forward to seeing -- while preserving that sense of innovation and novelty that makes a work fresh and exciting. Science fiction is a genre that is ideally suited to either trap or liberate an author. The difficulty arises in determining what precisely the specific elements are that appeal to the readers. It's easy to get lost in the minutia of science fiction, to focus on the appeal of the work at the wrong level of organization. There, the focus can go too high or too low; too detailed or too general. It takes a judicious hand to look at your own work and figure out what it is that your readers really like and then a lot of talent to re-create the elements your readers really like in a new work.

All this goes as a way of saying that Neal Asher has managed to hone in on what makes his work strong, re-invent it in new novels and make it stronger -- and stranger. His latest novel, 'Cowl' reads, in many quite enjoyable ways, like his earlier novels. Monsters, big guns, huge battles, soulless men who find a soul, soulful women who find a purpose, it's all there. But Asher has figured out precisely what to change and what to keep the same. 'Cowl' is every bit as bracingly weird as any of Asher's earlier novels. It's very different from those novels in some innovative and fascinating ways. Yet it's also unmistakably Neal Asher. And fittingly enough, Asher has solved the sequel-writer's paradox in a novel of time travel that itself revolves around paradox.

From the onset, 'Cowl' offers all the elements that make for great science fiction. The world we are introduced to is barely comprehensible, but realized with language that connects at a visceral level. Polly is a fifteen-year old prostitute in a 22nd century that seems fine to her but is positively hellish by our standards. When a regular customer tags her with a tiny piece of high-tech, she begins to hear voices that give her tactical advice. Pursued by hired killers, she's lured to another piece of technology, which bonds itself to her. This piece of technology is organic and also helpful. It gets her out of difficult situations, but there's a catch. It's pulling her backwards in time towards something most unpleasant.

What Asher manages to do in 'Cowl' is take all the stylistic elements he used to make space opera so enjoyable and re-combine them in a tale of time travel that can only be called a Time Opera. 'Cowl' is nothing like any time travel novel I've ever read. Clashing factions of the far future vie for superiority through myriad branches of time and probability. High-tech firefights with nasty monsters and incredibly destructive weapons leap off the pages. Asher evokes the wonder and action of space opera in an entirely new milieu.

At the center of the novel is 'Cowl', a genetically engineered Frankenstein's monster. He's managed to shift himself back in time to avoid his creators, who are terrified at the potential in their own creation. He's gathering samples from throughout time by sending pieces of an organic time machine, the torbeast, into the future, where they attach themselves to victims. These victims are now able to travel in time -- but only in one direction, back, towards an ungentle fate at the hands of Cowl.

Asher's primary characters are Polly and Tack, a hired killer originally selected to kill Polly who finds himself being repeatedly re-programmed as he's found and re-purposed by the various factions. Asher creates each character with garish strokes that cleverly conceal the subtle changes he manages to bring to them in the course of the narrative. Since every portion of the novel is a gripping, thrilling set-piece of one kind or another, the attention to detail that makes the characters grow in rewarding ways is both welcome and surprising. And he takes the characters in interesting directions; the girls get tough and the guys get a heart. It's absolutely the opposite of what you'd expect in the bloodbath that unfolds, but it's the kind of surprise that makes readers very happy indeed.

Though 'Cowl' has little of the usual textures one finds in a time travel novel, Asher does offer the reader some very enjoyable tidbits. Since Asher's characters have been compared to James Bond -- by Asher himself in the text of the novels -- it's fitting and appropriate that young Ian Fleming plays a pivotal part in a sequence set in World War II. But he's not the only name to pop up in the course of events, and readers will enjoy the natural fashion in which other special guest stars make their appearances. Especially since they do much more than make an appearance; they play a part in the plotting and themselves are changed by the events of the novel.

An important aspect of this and other Asher novels that's easy to miss is his use of plotting points out of mysteries and spy thrillers. Revelations of treachery, duplicity, double agents and triple agents keep the story in mind-boggling mode and mesh perfectly with Asher's clever evocation of time travel technology and its implications. Amidst the frenzy, Asher finds and takes ample opportunities to surprise the reader with a plot twist -- as opposed to a character -- out of the work of Ian Fleming.

Horror genre readers who enjoy Asher's work for it's singular bloody-mindedness will be particularly pleased with 'Cowl'. This is not because of Asher's evocation of dinosaurs as monsters, though that won't hurt. No, it's because as a work of science fiction and time travel, 'Cowl' echoes the best work of H. P. Lovecraft viewed through a haze of methamphetamine-induced bloodlust. 'The Shadow Out of Time' is a good starting point, while the torbeast could easily do stand-in work for Lovecraft's Nyalarthotep, the Crawling Chaos. Cowl himself is a cosmic, conceptual terror.

For all the thought, plot and character packed into 'Cowl', it's a remarkably compact work. That's good news, because once you finish it, you'll be very tempted to re-read it immediately. Asher's entertainment is big-brained, yet has the innate appeal of a catchy hard rock guitar riff. My advice is to save it for a rainy day, or a time when time travel technology is available, so that you can relax, stretch out and savor Asher's skillful exuberance.