"Quietly in Their Sleep" and "The Death of Faith" are the same book.
Several books in this series have two different titles so be careful! There are places to check this, if you don't know them feel free to PM me.
I love this entire series! I love Venice, too, and keep a map nearby so I can follow Guido around. Its not necessary tho:) its very good story-telling, interesting characters you probably will look forward to following, I highly recommend this series.