Bridge over Troubled Water

Publisher's blurb:

Here we are near the bridge, the exchange takes place at midnight.
We'll get Walter back, on the condition that we give them back the damn book.
We've been thinking about what to do if this all goes wrong.
Lily runs the engine, she usually drives more than all of us put together and in much worse conditions than tonight.
Sean and I will meet them, the book in my leather bag. And we're both armed... just in case...
There shouldn't be any witnesses, except maybe that hobo lying by a fire below.