First light, Ascension morning. From the top of the tower at the College of the Transfiguration, voices rise in song.Felicity's delight turns to horror when a black-robed body hurtles over the precipice and lands at her feet, the strange emblem of a double-headed snake clutched in his hand.Matters grow murkier as Felicity and Antony, leading a youth pilgrimage through rural Wales, encounter the same sinister symbol as they travel. Lurking figures...