In this issue:
"A Rare Success against Alzheimer's": A gold-standard clinical trial provides evidence that diet, exercise and an active social life can help prevent cognitive decline.
"How to Swallow a Sun": New techniques reveal how supermassive black holes shred entire stars.
"Transformers": By reprogramming DNA inside harmful microbes, biologists are turning them into patient-saving drugs.
"Evolution at the Limits": Studies of fishes that inhabit toxic sulfide springs reveal mechanisms of natural selection.