Talk to your city rep in your faction's tent. You must have completed the entire Aspirant quest line, including the Aspirant's Challenge, to take part in this quest.
Your rep will inform you that some brave crusaders have set up a camp in the Court of Bones, just outside Icecrown Citadel, and it's your charge to head there and help them out.
The camp is just outside past Corp'rethar, the Horror Gate.
Upon arriving, you'll find a whole bunch of crusaders and a pack of stabled Campaign Warhorses. These are your mounts. The warhorses, not the crusaders.
Mount up and head north. The area is lousy with gargoyles, labeled Boneguard Scouts, who'll be your first target. They're very easy to kill -- simply use your Shield-Breaker ability twice and they'll be dead. Kill ten of these to complete your first objective.
Next up are masses of Boneguard Footmen. They'll come after you in groups, but the good news is that these are incredibly easy to kill. Just trample them with your horse! You don't even need to use a skill, just run them through.
Finally, defeat three mounted Boneguard Lieutenants. These guys start off with one stack of Defend, so pull them with a Shield-Breaker and cut them down. You may get some Footmen along with them, but they pose no threat. And make sure not to pull the Boneguard Commanders with them -- they're a little tough for a Valiant to beat and you don't get any quest credit for them.
When you're done, just outside of Corp'rethar is the The Conflagration, a great area to pick up your Field Training credit (10 Scourge slain) if you haven't gotten it yet.
With those objectives completed, head back to your faction's tent and receive your reward.
Reward: Valiant's Seal x1 and 13g 23s