What have you got to lose by making the attempt?I just bought Open Secrets at a bookstore a few days ago, because it grabbed my attention, but I haven't read any of the other Vanguard books. Some series don't absolutely require that you read the prior installments to know what is going on, but I am starting to get the impression that I will be hopelessly lost not having read the others. Is that the case, and should I order the older books before attempting to read the latest one?

Open Secrets has several pages of recap right up front. Really, you should not be hopelessly lost.