Siblings tend to lions at a Tanzanian animal clinic.

"Eleven years her senior, Derek left America when she was fourteen to study and work in New Zealand, Greenland, and Chad, combing lakes for pale bacterial blooms. Over a decade Diana had collected his letters, filled with descriptions of the origins of rivers, dead fish in the Niantic, elephant calves strung up in abattoirs. And when she finished her sophomore year, he founded the Keren Reserve, a lion research conservatory that commanded a half-million acres at the edge of the Sahel. He had filmed four documentaries for television. Now, he researched emerging atavistic traits in the prides: infighting, cubs abandoned by their mothers."