When billionaire CEO Jackson Rand invites chemist Emma Caldridge on a humanitarian mission to deliver vaccines to villages in Africa, she jumps at the chance. But two weeks into the mission Emma, Rand, and his secretary are ambushed on the road to Dakar by a crew of assassins. When Emma drills Rand, he admits that he feared just such an attack, because the US government had hired Rand's company to secure the last known vials of live smallpox virus, and several insurgent groups were seeking it for use as a biological weapon. He tells her that some of the smallpox vials were found hidden among the vaccines, but claims to have contained them all. Emma calls Edward Banner, a defense contractor, for assistance and he relays some additional frightening news—three different insurgent groups are massing at the borders all around them, burning villages and kidnapping any Westerners in their path. Surrounded and with no way to break through to Dakar, Emma heads toward a refugee camp on the border, finding and freeing enslaved hostages along the route, and enraging the insurgents, who begin tracking her. While on the road, she discovers that a smallpox vial is close, the insurgents know it, and soon she's leading a ragtag group north through the Sahara Desert in a desperate bid to keep the vial safe and to reach Morocco and freedom.