In 1987, a scientist watched thousands of dazzling orange golden toads mating in a Costa Rican cloud forest. Two years later, she found a single solitary male, and then the species was gone forever. This episode is a biological locked-room mystery: how does a thriving species in a protected reserve, isolated from bulldozers and logging, simply blink out of existence?

We explore the toad's hyper-specific habitat, its hermit-like underground life, and the chaotic "explosive breeding" in puddles the size of a kitchen sink. Then we examine the suspects: an El Nino-driven drought that dried the breeding pools, and the chytrid fungus that has devastated amphibians worldwide. The competing hypotheses, from a thermal-optimum microclimate to a coincidental plague, leave the case tantalizingly unsolved.

• Why the toads were invisible most of ...