Blood Flag by Steve Martini

Blood Flag picks up the story of San Diego lawyer Paul Madriani. Paul's newest client is a woman, Emma, whose elderly father died suddenly. She says she had nothing to do with it, the cops think otherwise. When Paul sends his young assistant over to pick up the client's dog, the assistant vanishes. Then Paul hears from Tony, the son of a soldier who served with the Emma's father during the war. His father has also died under "iffy" circumstances, as did a third soldier they served with.

So Paul is trying to find out what really happened to these three soldiers, save Emma, and find his missing assistant. And it all eventually ties into a mysterious German blood flag that, if authenticated, is worth a fortune.

It's a quick read.