Councilor Halgrive (not Hargrove, as I mistakenly read it at first) needs to be talked to early in Plague's end quest. RuneScape players on the day of the quest's release were searching for him throughout East Ardougne as the quest guide itself didn't exactly say where in East Ardougne Councilor halgrive actually was.
It is easy to get to Ardougne. Home teleport puts you east of the city. Ardougne teleport puts you in the center market place. Other teleport methods bring you near to there.
Go west of the marketplace to the church. The church is seen on the minimap because it has a prayer alter. Look for Councilor halgrive in the premises. He is dressed in blue.
I found him in the graveyard, after first talking to Leo and going through a funny chat dialogue about his incompetence doing his job. Councilor halgrive had wandered just out of sight, so I missed him initially. I got lucky and clicked on him before I left the area.
RuneScape players want to complete Plague's End quest now so that when the new and long awaited elf city opens, they can be ready to access it. The quest has moderately high level requirements, needing level 75 in multiple skills. Elf City promises to become the high level player hub when it opens. Thus, players will want to complete the quest while they can. The plague's end quest has multiple prerequisites, requiring many hours of prerequisite questing for new RuneScape players and RuneScape players who have not completed a lot of quests in the elf city series.
Finding Councilor Halgrive shouldn't make a fun quest turn into frustration. The church is east of the palace, on the east side of the river, south of the agility shortcut. The general store is just to the south of the ardougne church and councilor Halgrive.