Read on if you dare! That is the epigraph in the journal found by bookbinder Lilian "Lily" Delaney when her friend, mentor, and partner John Caxton disappears. In the Oxford summer of 1903, while searching in his study for clues, Lily finds a hidden journal full of coded messages, written by Mr. Caxton 40 years before. As Lily digs deeper, rumours surface of a secret society he belonged to in his university days and tales the mythical, heretical book Liber Numerorum. But Lily is not the only one looking for Mr. Caxton. As she learns more of Mr. Caxton’s past, Lily begins to suspect her kindly mentor is anything but. When a member of his old university society is killed before her eyes, Lily fears Mr. Caxton will be next if she doesn’t find him soon. But even if she does, will he still be the same man she knew?

Lilian ("Lily") Delaney, apprentice to a master bookbinder in Oxford in 1901, chafes at the confines of her life. She is trapped between the oppressiveness of her father’s failing bookshop and still being an apprentice in a man’s profession. But when she’s given a burned book during a visit to a collector, she finds a 50-year-old letter speaking of love, fortune and murder. Lily is pulled into the mystery of the young lovers, a story of forbidden love, and discovers there are more books and more hidden pages telling their story. Lilian becomes obsessed with the story, but she is not the only one looking for the remaining books. With sinister forces closing in, willing to do anything for the books, Lilian’s world begins to fall apart, and she must decide if uncovering the truth is worth the risk to her own life.