London, 1583. The loyal courtier Simon Ames is viciously beaten. Is the attack random, or has Ames been the victim of a subtly treasonous act? A nonsense poem written by the lunatic Tom O'Bedlam has become a favourite of London's ballad sellers. Who has taken the meanderings of a madman so seriously and why? Following a trail of murder, treason and terror, Ames sets out to find the truth. But as he digs deeper into the human midden that is Elizabethan London, the puzzle becomes an enigma, then a riddle.