A silver shape went darting past him, sprinting down the alley and throwing back the darkness in its path. There was a split second when the dementor truly came into view, before it cast itself up and away into the air, disappearing amongst the clouds and stars. The shape turned, and began to sprint back towards Harry, and he could finally see that the patronus was in fact an enormous shaggy wolf, its lips curled back in a furious snarl as it charged towards the second dementor that had been approaching from behind. It too fled at the wolf’s approach, flying high and melting into the night sky.