I think one of the reasons I wasn't really into this book was because I'd just read a couple of books in the Danger Zone series by David Gilman and found this book to be quite similar in a lot of aspects: both boys the same age, absentee parents they have to rescue, involving following clues left behind for them. While this book has an interesting premise, I found the writing to be a bit sloppy with the overuse of certain phrases and the story to be predicatable. For example, as soon as Matt saw photos of a girl 'who looked a lot like Robin', I could tell where that line of the story was headed. It wasn't hard to make out other parts of the plot.
I also found there to be little character development, particularly in Matt but also in Robin. For someone who is hiding a secret like hers, she wasn't very particular about hiding it, dropping clues so often I thought Matt had to be quite 'daft', as they say, to not realise. It also seemed that Matt had almost forgotten or disregarded the fact that his father was missing (I think this is the fault of the poor writing) once he started searching for the treasure, and so did everyone else. This frustrated me because this was supposed to be the whole point of the story, not just a "oh, what about Dad?" moment dropped in here and there.
The novel also seemed to be unfinished. Did I miss the significance of Smith's blue eyes? Couldn't work that one yet. I would say Richards was probably leaving himself open for a sequel.