A burning fishing boat found on the Channel turns into a new case for Karl and Elise.
A shocking discovery is made at an immigration removal centre alongside a sinister animation containing a hidden message.
The investigation steps up when Winnie is sent a live rat in a box, with a set of co-ordinates leading to the Pied Piper's latest victim.
As a young mother-to-be helps with their enquiries, a new development threatens to tear Karl and Elise's partnership apart.
Karl makes a foreboding discovery at Elise's apartment, and the pattern of missing people continues.
In the final episode, Karl and Elise face a tense and gripping showdown with the Pied Piper, while the truth about the Moreau abduction is revealed at last.