It's not uncommon when reading a thriller to get a feeling that it's been written to be filmed - clues are a big car chase leading up to the climax, and the hero(ine) wandering round a dark, empty building at night with no idea what else is hiding in the darkness.
This, though is the first book I've read which felt more like a literary version of a computer game, and I've been trying to work out why.
One reason I think is the non-specific locale. It's definitely not the author's Italy, but not quite America either, so the impression is of a world not quite as we know it. (That might be a useful device for an author come to think of it - at least you don't need to worry about the anoraks writing to you to point out that a deputy in West Virginia isn't entitled to enter a deserted property without previously doing A, B or C).
Add to that the jump to different gothic locations, among them the huge, deserted orphanage and the vast mansion with a dying owner kept secluded from the world. Each of these seems to exist in isolation, as if we're moving from one stage to another, almost entirely separate, one.
Similarly with the villains - without giving too much away, various murders are solved along the way, done and dusted and put behind the team, but none of them is the big one, which remains unresolved up to (and possibly beyond) the big Game Over.
That all said and analysed, it must be admitted that on its own terms this is a terrific book. It's as if the author worked out what readers of this sort of book want, and resolved to give it them in spades. You want a serial killer? How about a series of serial killers? A mole in the investigating team? Yep, let's have two or three of those. A twist in the tail? No problem; plus a couple before that as well. Oh, and I know you didn't ask, but let's have a medium as well; in this case a medium communing with someone who isn't actually dead yet.
The only thing is, I can't really see where the author can go from here - he seems to have poured into this one as much as you'd expect to find in an entire series.
All in all, if you like restraint and realism in your crime fiction, this probably isn't your cup of tea; if on the other hand you enjoy an over-the-top romp with no holds barred and a creepy atmosphere sustained through the entire book, with the likelihood that the ground is going to be cut away from under your feet at any time, then give it a go.
(By the way, to those who say that the central conceit was borrowed from Agatha Christie - maybe it was, but she borrowed it from Shakespeare's Othello anyway. A good idea is always worth rehashing).