I only remember this as a program watched 38 years ago but I was struck at the time how the feet-on-the-ground, methodical approach to why China had such a high incidence of esophageal cancer. This was low tech, logic at its very best: step by step, paper and pencil, maps and the researchers got closer and closer to finding where, when and why people were dying of this cancer. The unbelievable answer was a particular pickle, prepared in a particular way that showed, without a doubt, the cause.
For lovers of logic puzzles instead of high tech, high cost research it doesn't get any better than this.