The Dream Thief is the fourth book in the Horatio Lyle series. You could read this without having read the others, though I'd advise you to try the others first because this is easily the weakest entry so far.
Special Constable Horatio Lyle, man of science and sort-of foster father to reformed pickpocket Tess, opens his door one night to find a poisoned child unconscious on his doorstep. Tess recognizes the girl, Sissy, as an inhabitant of the workhouse she ran away from. Despite Lyle's best efforts Sissy won't wake, and when he begins investigating with the help of Tess and his other young friend, Thomas, he uncovers a racket involving workhouses, orphanages, a circus and inexplicable kindness to the children society doesn't want. But who is poisoning the children into emptiness and sleep, and why? And when Lyle's own life is on the line, who's going to save him?
Had I known that there was a creepy circus in this book, it's entirely possible I would have decided against reading it. I hate circuses, especially creepy ones, and the description on the back of this book really doesn't tell you what you're in for. Apart from the ick factor (and I do mean ick, because as always the gore factor is low), I just found this book unsatisfying and wondered if Webb got bored halfway through and couldn't be bothered finishing it to her usual high standards. The concept of Greybags didn't work for me and his story was resolved unsatisfactorily, there were plot holes, some of the action scenes didn't make much sense and not every loose end was tied up. The ultimate villain's motivation might be believable, but when that character has had so little face time and everything's explained in an infodump towards the end, it just feels meaningless. Tess' speech patterns have changed - she's suddenly talking more like Ali G than a Victorian urchin - and her rants against injustice feel more like authorial grandstanding than something Tess would actually say (and offer no solutions, either). The cameo by Marx plays no role in the story and seems attributable solely to Webb's desire to appear clever. The romance between Lyle and the annoying Lin Zi - was I supposed to take that seriously? It came out of nowhere and felt like an attack of the artificial happy endings, with a distinct flavour of "the series ends here". On the upside, though, Thomas is a more active, harder-edged participant in the story this time round.
If this is the last book in the series, I think that really would be a shame, because the characters still have a lot to offer, 1860s London provides an awful lot of material for future books and Webb is a genuinely talented writer. But if there is to be another book, I hope she takes her time, really thinks it through and provides a much better story than this.
On a final note, the lame CGI cover, which doesn't fit with the previous covers and gets Tess badly wrong, and the reuse of the chapter-heading pictures from The Extraordinary and Unusual Adventures of Horatio Lyle give the impression that the publishing company, too, didn't make much of an effort with this.
Suitable for children aged 12 and upwards, due to complex language. No sex, no swearing, limited violence that has consequences.