In the wake of Eamon Cunningham’s death, the Kinsella family is thriving. However a new threat rears its head when members of a Turkish cartel inform the Kinsellas that Eamon owed a them sizable debt – and since they killed him, the debt is now theirs. Elsewhere, Viking is released from prison intent on making trouble, Amanda suffers a personal tragedy, and a looming presence from inside the family returns.
　　The new season will see the Kinsellas at the top of the game in Dublin, but killing Eamon Cunningham has created as many problems as it solved. They have incurred the wrath of an enemy even more dangerous than him. And where once there were unbreakable bonds of blood and family, now there is only suspicion, distrust, and resentment. But the greatest threat to the family emerges from within: in the shape of a ruthless, bullying, agent of chaos. Fortunately, from positions of great adversity the boldest plans are often forged. And so it is with the Kinsellas.
　　Returning cast includes Charlie Cox (Daredevil), Clare Dunne (Herself), Aidan Gillen (Game of Thrones), Sam Keeley (Joe vs Carole), Emmett J. Scanlan (Peaky Blinders), Maria Doyle Kennedy (Outlander), and Yasmin Seky. Francis Magee also returns this season.

八年前，一个名为堡垒的独立全球间谍机构，被新兴的犯罪集团曼提柯尔所摧毁。精英特工梅森·凯恩（理查德·麦登 饰）和纳迪亚·辛格 （朴雅卡·乔普拉 饰）死里逃生，而他们的记忆也被抹去。八年后，梅森的前同事伯纳德·奥立克（斯坦利·图齐 饰）请求他帮忙阻止曼提柯尔建立新的世界秩序。