The Black Circle

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The Black Circle is the fifth book in The 39 Clues series and is written by Patrick Carman. This book was released on August 11, 2009. Amy and Dan Cahill, the protagonists of the series, try to follow a Lucian secret which was stolen by the Nazis during World War II. They also encounter the infamous Madrigals who helped them escape the Black Circle in the end.
The Black Circle was selected as Al Roker's book club pick.