Grüfeld Bach is a Saradominist priest who is part of an Saradominst order to track down an evil Zamorakian wizard named Denath. He is also the descendant of many great demon slayers who had all once slain the demonDelrith with the sword Silverlight. During Demon Slayer, he recurits the player at a Saradominist church to help stop Denath, who has stolen a book of demonology from Edgeville Monastery to summon Delrith, by having him/her pass his ancestors' trials to obtain Silverlight while he tracks down Denath.
Once they both complete their missions, Bach tells the player that Denath is located in a crypt of a Zamorakian church in southeastern Varrock. They kill the monks of Zamorak working with Denath and when they kill the last monk, they hear from Denath that he has completed the ritual already and teleports away right before Delrith arrives. Delrith injures Bach with a magical attack but Bach manages to create a protective barrier around him that protect him and the player from Delrith's devastating attacks. Eventually, Bach and the player defeat Delrith and re-seal him and the crypt starts to collapse. Bach teleports them both out back to the Saradominist church and rewards the player with Silverlight.