Lady Liadrin is the leader of the Blood Knights and is currently located in Shattrath City. The Blood Knights are an order of former priests and warriors who use the Light magics from the enslaved naaru M'uru. Liadrin herself, a former elven priestess, became disillusioned with the Light following the Fall of Quel'Thalas. She had long forsaken her Light-given powers when M'uru was transported to Silvermoon following the capture of Tempest Keep. Magister Astalor Bloodsworn proposed using the naaru's powers to bestow certain blood elves with the powers of paladins. Liadrin was the first to volunteer to make use of these powers, and thus she became the first and leader of the Blood Knights.
Her solitude can be an underestimate of her power. Once you enter battle, her speed is immense and her attack power is high enough to take a well-geared level 70 player down in a matter of seconds. Although, with a well-geared healer with a high amount of mana per 5 seconds, you can take Liadrin down with three people. A tank, a healer, and a dps or two. Be aware that with three people it is a very long fight, around 15-20 minutes, but the reward is great. She drops anywhere from 60 gold to 100 gold.
The being M'uru, also in the chamber, is a friendly unit to Alliance members and will not aid in the attack, even if the beams from the magi are broken.