Sarah nods. It pretty much tracks with what they know at home—and Helena, presumably, is the same as she is. Immune to the clone disease, able to have kids. "It's just random," she says again, to Helena. "That we don't have whatever causes the disease. And Kira doesn't, either."

She glances to Cosima and adds, "We were actually using stem cells from her baby teeth as a treatment for you, and then bone marrow..." She trails off, not wanting to say the rest, but it's probably obvious by the look in her face that whatever happened didn't work. (Thanks, Rachel.)