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.

A body falls from the fourth storey of a construction site. Was it just a terrible accident, or a perfectly executed murder? John's team think he's losing his touch when he latches on to a far-fetched theory and starts pointing fingers. When things don't quite add up, John begins to question his abilities both at work and at home, whilst Lucy's frustration at their lack of progress in finding her husband reaches fever-pitch.