After hearing of the atrocities committed by the Mourners, a shocked Halgrive will believe the player and task them to control the situation within West Ardougne, due to the reputation of the adventurer and the futility of doing anything in his position without being stonewalled or "diagnosed" with the plague. In a official capacity representing the authority of the city council, he will also produce a proclamation that handles control of the East Ardougne army to the player to support the revolution and the removal of King Lathas.
This article on an NPC has an associated dialogue page. Click here for a transcript of possible conversations with this NPC.
Although he is part of the Ardougne City Council, he, like most of the citizens of East Ardougne, was initially oblivious to Lathas's evil plan of getting rid of his own brother, King Tyras.
Should full mourner gear be worn, he will ask the player to raise the issue of the infected sheep to the Head Mourner, as he is worried that containment is not working.