Turn right and then right again into an alcove for the next treasure; 7x Begrimed Claws . Turn around, go down the stairs and confront the PSICOM patrol. Two PSICOM Rangers will be accompanied by a Crusader (a tougher Myrmidon). Kill the Rangers first because, while weak on their own, they can bestow buffs on the other enemies. Crusaders are easily Staggered but have powerful and quick attacks. Always aim for preemptive strikes where possible to take advantage of Stagger, though do not waste Deceptisol on these enemies.
Another similar group lies just beyond the first one and they are also guarding a Treasure Sphere containing a Spark Ring (improves Lightning resistance) which will be very useful in the upcoming boss fight. Follow the marker to the next section.