The second book in a series can go wrong in two ways... it can either differ so much from the original that it loses what ever it originally had going for it, or you can find yourself reading a book that is exactly like the first, with no real change in characters or plot, a very common trait in books based around murders and mysteries. The ideal is that a second book should develop on its characters, changing their circumstances in a way that causes them to grow and relate to each other and their world differently. The plot needs to be new, but also carry with it an escalation of some greater plot that will come to a head at the end of the series.
For me, this is what Bloodhound did perfectly. The change of setting and development in characters was both believable and interesting. The plot line, if it is possible, was even more gripping than the last.