I have fond memories of this book and it's a pity they haven't reprinted it (at least not recently). I've been looking for more challenging puzzle books with beautiful illustrations but it seems that most of the recommended ones are printed in black and white or grayscale, which pale in comparison to the lovely and compelling illustrations in this book (I love how there was a consistent art theme for each investigator), or are glossy/expensive enough to discourage me from writing marginal notes in pencil, at the very least. If anyone has a good recommendation, please send me a PM!
These are actually really difficult. They were written before the preponderence of Sudoku-esque logic puzzles, and a lot of them rely on you drawing out your own logic grids to match answers to each other. I stalled on it for a long time - actually because I started it before I moved house and then... forgot to continue it after I moved. For three years. Good going there. I think I also failed one of the puzzles and it put me off for ages.
I much prefer Map and Maze Puzzles, although I now suspect that one has a serious error in the final puzzle.
I have loved this book for ages. Some of the puzzles STILL trip me up, but many of them have become silly little things to occupy a thoughtful child for a few minutes.