The fourth series is acclaimed French crime drama Spiral, original French title Engrenages, will get a UK DVD release on March 18th.
Currently airing on BBC Four, the 12 episode series finds Laure (Caroline Proust) and her team investigating the death of a student who was apparently killed by a homemade bomb.
Meanwhile lawyer Joséphine Karlsson (Audrey Fleurot) is getting herself into dangerous waters defending undocumented immigrants; her colleague and Pierre Clément (Grégory Fitoussi), surprisingly finds himself representing crime boss, Johnny Jorkal.
Meanwhile Judge Roban (Philippe Duclos) 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 in another tense and gripping series.