Hidden

Hidden was one of the early Torchwood audiobooks, read nicely by Naoko Mori (a.k.a., Tosh). It's a very unusual Torchwood story in that, as far as I can remember, it has absolutely nothing to do with aliens or alien artifacts (Countrycide is the only other example that comes to mind of a Torchwood story that meets the same criterion). It's actually more in the Dan Brown (The Da Vinci Code) style, as it involves an ancient arcane mystery (in this case, alchemy), a Templar-like secret society of masked gunmen willing to kill to keep their secrets, and a couple of brutal car chases (one of which leaves Ianto a bloody pulp). Also unusual for Torchwood is that Jack has more of a background role (he spends most of the time in a police interrogation room). On the whole, I'd probably give it an average grade--definitely better than Everyone Says Hello, but not as good as The Sin Eaters.