"Alastair! Come help me!"
I spun around and sprinted down a slope of broken granite, when a whiff of something toxic temporarily blinded me. Confused, rushing, I tripped down the scree to find Gemma doubled over, screaming, a quivering hand held up covered in orange oil. "What's happened to you!" Strolling down from the summit of Half Dome an hour earlier, our tallest big wall climb to date, we thought all the difficulties were over. Who would have known the last two hours to the valley floor would prove to be the crux.