Born joined at the pelvis, Siamese twins Dao and Duan were brought to the United States from Thailand to assess their chances for being separated surgically. NOVA covers the intricate planning and protracted operations that eventually made the two girls into two distinct individuals.

A massive planet-sized machine controls our weather day-to-day, and our climate season-to-season. It takes an event of staggering proportions to disrupt a machine this large and powerful, a juggernaut with more energy than a million nuclear bombs. Signs now indicate that such an event is underway - El Niño. More than a series of storms stunning the California coastline, El Niño is second only to the seasons in its effect on global weather. In a P-3 off the coast, a team plunges into a storm front to explore its cause and effects. In a boat off the Galapagos, an array of buoys are checked for temperature and current data. On a mountan in Peru, signs of the devastation of past El Niños are revealed. As scientists push to extremes to explore this phenomenon, they understand for the first time the extent to which all the world's weather is connected, and just how delicate is the balance.