Are these sentences worded in the correct way?

FYI- The demon serves Sammaster's agent, the sunwyrm. Taegan and Jivex battled the demon on multiple occasions in their investigation to discover the traitor, and they eventually discovered that Sammaster’s agent was a sunwyrm who was magically disguised as the human wizard Phourkyn One-Eye, but not before its demonic assassin murdered another one of the Thentian mages. The two companions defeated the sunwyrm with the aid of several of the arcanists, but Rilitar soon died from the wounds that he sustained during the fight. (The Rite)