Te Bounty by Janet Evanovich and Steve Hamilton

 The Bounty is part of the Fox and O'Hare series, which I am new to. (And this is not the first book in the series.) Kate is an FBI agent who has been teamed up with con artist Nick. In this book, both of their fathers get involved in their caper. The whole story is a treasure hunt for a mother lode of gold bars stolen by the Nazis.The group, along with a professor who is helping them decipher the clues (written in German) keeps finding parts of a treasure map that will hopefully lead them to the gold. At the same time, they are being chased by a nefarious group called The Brotherhood, that also wants to get its hands on the stolen gold.

It's an entertaining tale though I have to say the way they escaped some of the dangerous situations they found themselves in kind of stretched the bounds of credibility.