On the Syria/Iraq border a British hostage is beheaded by IS terrorists. When the executioner breaks down he is led into a nearby tent where a masked figure is waiting for him. This mysterious person is treated with a mixture of respect and terror. They call him the Caliph.
In Nigeria the British Ambassador and his young aide are kidnapped. A four-person SAS team is deployed to find him. The team find devastation in Nigeria, and when they discover prisoners infected with the plague they realise they have uncovered a combined Boko Harem/IS plot to unleash a bio-terrorist attack upon the world.
The team must stop the terrorists and identify the Caliph before the deadly disease is threatens those much closer to home.