Day of the Winter Solstice

Bilbao is engulfed in panic. A serial killer has appeared in the city.

N9 kills with brutality and each time leaves not only a corpse, but also a clue to long-forgotten, unsolved cases. It seems that N9 deliberately helps the police by eliminating those who he believes should be dead.
Inspector Ander Crespo from the Ertzaintza gets drawn into a nightmarish game in which the maniac leads him by the hand to the truth. But what price will he have to pay for this assistance? And how are N9's victims connected to the missing girls?
As Bilbao plunges into darkness, Ander must understand: to catch N9, he will have to confront a horrifying past.