CALLING ALL CAHILLS! Announcing a 39 Clues Superspecial adventure -- the gang is back, and called to investigate one of their own: Sinead Starling.A TRAITOR RETURNSThe Cahills are the most powerful family history has ever known. For the past five centuries, they have secretly served as guardians of the world. The Cahills command presidents, take down corrupt governments... and are currently led by a fourteen-year-old boy with a superhero complex.Dan Cahill may be young, but he's nobody's fool. So he knows he must act fast when he learns that Sinead Starling, a former friend who betrayed the family, is up to her eyeballs in a plot to control a deadly virus. But is Sinead behind the plot, or is she a hero trying to stop the virus from getting out? The search for Sinead will take Dan and his friends from Cuba to the Bermuda Triangle, where the fate of the world may just depend on whether the Cahills can trust a traitor...