Polaris

A dreamer splits his waking attention between an ordinary modern home and a post he keeps watch from in an ancient arctic city under siege, uncertain for most of the account which life is the dream. Lulled to sleep at his watchtower by the Pole Star's voice at the exact moment his warning is needed most, he wakes to find his city's fate sealed and no way to prove — to himself least of all — which of his two lives was ever the real one.