"Yes, I know, that's where I was going," she says testily, continuing her grim forward motion towards the tree-shaded clearing at the edge of the park. It is lovely here, the ground dappled in what light filters its way through the leaves overhead, and Harrow looks for a spot that's clear and flat enough.

"There," she says, pointing at a space just in front of one broad trunk. "You did remember to bring a blanket, right?"