Laine hands you a rock disguise he finds on the farm. You head to the mine with it, and sooner or later, you get to the back of the mine and hide in the rock. While you're attempting to either stay hidden or exit the rock—both of which have the same result, namely keeping you stuck in the rock—you overhear a woman's voice say one sentence: "Sentinel Hill will burn for what Stormwind did to us."
As soon as you can get yourself out of the rock, find out where Sentinel Hill is and warn its leader before the Hill burns. Take Laine's suggestion: Take the walk. Face the source of the threat.