Regie : Robert McKillop, Mit : Anna Maxwell Martin, Ralph Ineson, David Mitchell,

After a breakthrough finding a coded notebook, John decides to return to the police station to gather more information about his missing brother's last case. Before John can make much progress, his thirst for all things cryptic sees him drawn to another grisly crime scene at a grand manor house. What looks like a missing person's case turns into something far more sinister as John puts his puzzle mind to work. Back at home, a frustrated Lucy takes matters into her own hands and embarks on a fact-finding mission to the home of one of her husband's ex-colleagues.