Series One finds Molly Dawes (Lacey Turner) taking on the challenge of serving as an army medic in Afghanistan. Thrilled to be on the front line, she gets off to a bad start with her platoon leader 
Captain James (Ben Aldridge).

Series Two introduces Michelle Keegan as Georgie Lane replacing Molly, with Two Section now posted to Kenya. Serving at a refugee camp on the border of Somalia, Georgie becomes enmeshed in a dangerous situation and all too quickly finds herself a hostage of Al Shabaab.

Series Three sees Georgie in a post-earthquake Nepal where the past catches up with her. In Nigeria, she comes up against the terrorist group Boko Haram. Recuperating in Belize, Two Section undertake a jungle training exercise which becomes deadly and a refugee crisis in Bangladesh takes them into danger as they try to help in a troubled land.

Series Four and Georgie faces her darkest demons when she returns to Afghanistan, alongside new recruits and trainee medic Mimi. A suicide attack instigated by an old nemesis causes questions to be raised about Georgie's future in the army, but with her career hanging in the balance, will her instincts be trusted?