A fourth series consists of ten episodes. Scott and Stonebridge are recalled from holiday in California to capture Leo Kamali (Zubin Varla), a high ranking member of a terrorist cell led by al-Zuhari, an elusive terrorist. After capturing him in Colombia it is revealed that Kamali is working deep cover with the CIA to stop al-Zuhari. As Kamali is pressured to work with Section 20, Dalton is suspended by Colonel Philip Locke (Robson Green), who takes charge. Dalton is later killed by the Real Irish Republican Army (IRA), who have joined forces with al-Zuhari's group. In the meantime, Scott and Stonebridge are wanted by the Russian mafia after killing the son of mob boss Arkady Ulyanov in Colombia.
The third series consists of ten episodes. Former military intelligence operative, Major Rachel Dalton takes charge of Section 20. They work throughout Africa to gain their hands on four nuclear triggers which are in the wrong hands after a mission in Somalia. The triggers have originally been sold to Conrad Knox (Charles Dance), an English billionaire and philanthropist based in South Africa, who runs the Knox Foundation, charged with disarming unstable regions. However, it becomes apparent that he is using the weapons to arm his own militia, and is using the triggers to build nuclear weapons with the intent on liberating Africa "to a point where its voice is not just heard but listened to." Due to Knox's influence, Section 20 is forced to go dark to stop him. In the meantime Stonebridge seeks revenge on Craig Hanson (Shane Taylor) for murdering his wife, and Scott has to contend with Central Intelligence Agency (CIA) agent Christy Bryant (Stephanie Vogt), whom he used to work contract killings with. By the conclusion of the series, two of the bombs are recovered, and the remaining two were disarmed before they could destroy Johannesburg, Stonebridge fulfils his revenge, and Knox kills himself when he fails.
The second series consists of ten episodes. Porter is captured by a Pakistani terrorist called Latif (Jimi Mistry) while investigating a planned operation of Latif, Project Dawn. Sergeant Michael Stonebridge (Philip Winchester) finds disgraced ex-Delta Force operative Damian Scott (Sullivan Stapleton), who would not be hired by even private military contractors, who previously worked with Porter to track Latif. After Porter is executed, Section 20 discover Porter left the team clues to a hotel in New Delhi, India, where a group of terrorists attempt to capture a weapons scientist with knowledge of hidden weapons of mass destruction originally used to plant in Iraq, which serves as a part of Project Dawn. The weapon, namely VX nerve gas was kept in storage, and Latif has known about its existence.
As members of a top-secret anti-terrorist organization, British sergeant Michael Stonebridge and disgraced Delta Forces operative Damian Scott form an unlikely alliance aimed at stopping a scheming international terrorist in this Cinemax series.