Continued exploring cavern without hesitation. The southernmost corridor led straight to the quarters of the grimlock High Priest of Erythnul. We discovered him perched atop a high ledge, seemingly completely oblivious to our presence. The same could not be said of his fanatical guards, who attacked immediately.
The speed with which we dealt with his personal guard apparently convinced the High Priest that we were worthy oppenents. He dropped down from his perch to engage us, but not before becoming invisible. This tactical advantage was short-lived, as he became visible upon his first attack.
The battle was short and decisive, and we emerged victorious.