7: Clockwork Angel (The Infernal Devices Book One), by Cassandra Clare (2010 hardcover)

The first of Cassandra Clare's books I read were those in The Mortal Instruments series: City of Bones (2007), City of Ashes (2008), and City of Glass (2009). In this trilogy, Clare explores the world of Downlanders and Shadowhunters--the creatures of the dark world (vampires, faeries, werewolves, demons, etc.) and the warrior force that enforces a treaty protecting humans from these supernatural beings. In the Instruments series, the protagonist and heroine is a teenage girl who suddenly develops the ability to see these beings in the other realm, usually invisible to humans. Her quest to understand why she has this ability and how to find her mother--apparently kidnapped from someone within the shadow world--takes her from the streets of New York, to London, and eventually the Shadowhunter city of Idris. 

Clockwork Angel is a Prequel to the Instruments books, the first of The Infernal Devices series.  Like the Instruments series, the protagonist is an American teenager.  Tessa's entry to the hidden world of Downlanders is less accidental, however.  She is kidnapped upon disembarking the ship bringing her to England to see her brother and is held by warlocks in hope of developing her here-to-unknown powers of shapeshifting. Rescued from her captor, Tessa is taken in by Shadowhunters and is swept up in the battle of good versus evil raging outside the view of most humans.

Set in Victorian London, this book further develops the history hinted at in the earlier trilogy, while continuing similar themes of the supernatural, the use and abuse of power, and what it means to be human--all with the requisite teen love interest (the cute-boy rescuer, of course).  It's a bit Twilight meets Harry Potter, without Meyer's bad writing and hapless heroine and more violence than Rowland allows.  For folks enjoying fantasy writing that integrates the supernatural with the known world, it's a good read; both series have a strong female lead and enough fight scenes (including swords, knives, and magic) that it should appeal to teens of both genders as well.  I'd recommend starting with The Mortal Instruments series before picking this thread up.  However, Clockwork Angel stands on its own should you choose this as your entry to Clare's world.