When a charismatic stranger disturbs Tempus Penhallow’s less than exciting life at ancient Lethe Hall to inform him that his mother lied about his father’s death, Tempus ignores his tutor’s warning not to fall for the stranger’s bait and accepts his father’s Compendium, an intricately encrypted device, and follows his mother through a hidden door in Oxford University to find out what why she lied. The door, in All Soul’s College, leads to a much, much older university – where ideas never die and the souls that create them live on outside time and space. Barely surviving the university’s self-protective mechanisms, and having lost his mother’s trail, Tempus finds a room to hide in and surprises a young college scout, Rowena St Clair — precisely where she’s not supposed to be — reading books in the Master’s private library.

In exchange for his discretion she offers to help him, but their cautious alliance falters as soon as he introduces himself. The name of Penhallow has been forever blackened by Tempus’ father, believed to have stolen five Hallows of Time vital to the continued existence of the University. Phaedrus Penhallow had always taken a particular interest in Rowena, but when he abandoned her to fend for herself she’d never forgiven him. And she wasn’t the only one who felt betrayed.

His notoriety now tainted anyone who had ever called him friend — from the baker he bought his bread from to the Mazaalai knights who were sworn, like him, to protect the Hallows with their lives. Now the discredited knights take any work they’re offered in order to survive, the University is shrinking, time is out of joint, and Tempus discovers he’s the long-hunted scion of a dynasty of Hallow Guardians, gone bad.

With his cover blown and his life in danger, Tempus and Rowena risk everything to pursue the trail of codes and symbols in his father’s Compendium through the sealed crypts, dangerous catacombs and magical libraries of an alternative Elizabethan London to unlock the mystery of their families’ entangled pasts and restore the Hallows to their rightful place. But to succeed, Tempus must not only come to terms with his family’s conflicted history, but confront the source of ancient power that is his legacy.