"But paradise is locked and bolted…We must make a journey around the world to see if a back door has perhaps been left open" —Heinrich von Kleist, "On the Puppet Theater"
What's up with the epigraph?
The first thing that catches our attention with the epigraph is the mention of paradise. Fallen is chock full of references to the Garden of Eden in Genesis—that book in the Bible in which Adam and Eve go apple-picking and get in heaps of trouble. The idea of paradise being locked also plays a role in the Biblical allusion, because after Adam and Eve get caught eating from the Tree of Knowledge, God kicks their butts to the curb and locks the doors of paradise behind them.
There's also something subtler going on here. Luce, who is searching for the reason she feels attracted to Daniel, is looking for her own version of paradise in his recognition and his love, so she sneaks ever closer to him in hopes of unlocking these secrets—and the clues to Daniel's aloofness.
To do that, Luce might need that hefty ring of keys Penn carries around, because Daniel has more secrets than the number of locked doors at Sword & Cross.