Are these sentences worded correctly?

FYI- Gromph is the mage. Meanwhile, Gromph awakened in a cave near Menzoberranzan, but he was still trapped in the glass sphere. The mage escaped with the help of his rat familiar, Kyorli, and the illithid Sluuguth, whom Gromph promised great power too and then killed. Gromph immediately helped bolster the defense of Menzoberranzan against the duergar and tanuruuk armies that had reached and begun to besiege the city