They hadn’t seen the cairn the night before. Captain Williams pulled up the collar of her wool coat as the wind buffeted her and whipped up tiny cyclones of powdery snow and ice that stung her face. The lookout had roused her as soon as there was enough light to distinguish shapes. Perhaps on a normal mission suspicion wouldn’t have arisen so soon. But here in this barren, frozen heath, any anomaly on the horizon warranted investigation. The sun was high enough now, attempting to inject some color into the monotone world of ice and snow, that they could see it was a stone cairn, simple pile of large gray-brown…