Spiral has been an export success, with sales to broadcasters in more than 70 countries including Australia, Denmark, Finland, Italy, Japan, Mexico, Portugal, Switzerland, Spain and the United Kingdom.

As her identity and past life are gradually revealed by the investigating French justice system, it becomes apparent that her story ties to a network of corruption that may touch the people uncovering the truth about her.

When the mutilated body of a young woman is found on a disused railway track in the North of Paris, near La Villette, Captain Laure Berthaud takes the opportunity to restore her image after her involvement in the death of Mustapha Larbi.

She quickly thinks the murderer could be a serial killer, and her intuition is confirmed a few days later by the disappearance of a second young woman with the same physical appearance in the same neighbourhood.

Time is running out to avoid new victims but the investigation goes badly: Berthaud and her men make mistakes, losing the confidence of their hierarchy, whilst newspaper articles on the so-called "Butcher of la Villette" increase.

Moreover, the prestigious Criminal Brigade, led by Commissioner Vincent Brémont, Berthaud's former supervisor when she was a young police intern, now wants to get back the case.

In the meantime at the Palais de Justice, while investigating an ordinary case of a child attacked by a dog in the wealthy suburb of Villedieu, Judge Roban discovers that the mayor might be involved in a bribery scandal.

Prosecutor Machard immediately asks Pierre Clément to use his friendship with the judge to spy on him discreetly, in order to prevent a political scandal: the mayor of Villedieu is a personal friend of the President of France.

Police Captain Laure Berthaud and her lieutenants, Gilou and Tintin, investigate when, after his homemade bomb accidentally went off, a mortally wounded student is dumped by his accomplices in a Paris wood.

Lawyer Joséphine Karlsson is getting herself into dangerous waters defending undocumented immigrants; her colleague, Pierre Clément, surprisingly finds himself representing crime boss, Johnny Jorkal; while Judge Roban returns to the Palais de Justice, sidelined and on the warpath.

As the story unfolds to reveal a group of extremists intent on waging a war against the Parisian Gendarmerie and a dangerous arms trafficking operation, the police and the lawyers begin to turn on each other.

A double homicide in a Chinese restaurant in the 13th arrondissement leads to a wider story of money-laundering networks and governmental corruption.