The book is the second in a series.
Basically humans are considered too violent and shut off fromt he rest
of the galaxy
In the first book, a human investigator/troubleshooter helped solve
some mystery or something (I never read the first book)
In the second book the same character gets his team together and is
sent to another dimension where they meet some very violent aliens
(crabs?)
Sound familiar anyone? Sorry for the vague plot details which could be
wrong.