Even though he was able to parry one of Szara's claws, the drow was too slow to avoid the catgirl's other swipe, or Diomeera's blade.  The combined attacks left large gashes in his skin under the armor, and he quickly collapsed under the assault.  The second drow took a nervous step backwards, then circled around to swing at Diomeera.  He was too slow however, the paladin spinning around to block his blade as she finished removing it from the drow's former ally.