The slight magic imbued in that old parchment, written and delivered by the High King himself, was likely one of the handful of things in all the Stormfront that could have properly reached him. Without higher guidance, there was no chance of a crow finding its way to a man that it had never met, all this way underground.
"Now aren't you just the most majestic little creature?" Magnus said, scratching the crow under the neck, making tame the creature. It cawed at him happily, and Magnus cooed at it in turn. "Yes, yes. I too hate these winding tunnels, and their lack of light, and their emptiness. Too long we have spent in the past, little crow. What do you say we go on a little adventure, yes? The High King has bid that we help him, and perhaps we might. But who can force us to go directly there? Certainly no mortal man."