Hurricanes, floods, earthquakes, wars - all can trigger not just thousands of casualties and refugees, but also a worldwide humanitarian effort, with the roots for its success founded in science. At the Zaatari refugee camp, temporary home to around 90,000 Syrians, Maggie Philbin looks at the problems the humanitarian community faces when tackling a disaster, and how the lessons learned there might help closer to home. Liz Bonnin comes face to face with cholera, one of the most feared bacteria on the planet. And the team are joined by Dr Chris Van Tulleken, who makes Plumpy'nut, a simple peanut-based paste that has saved tens of thousands of famine victims.