The b side says 'Remove each other location in play from the game'. Enemies or other cards in such locations are removed as well? I understand so, although there's the bad default rule too...
Objective - If each undefeated investigator is in Walter Gilman's Room, investigators may spend the requisite number of clues, as a group, to advance.
Specter of the Past - Back
Swap Walter Gilman's Room with the set-aside Keziah's Room, taking its place (all tokens and cards at the former location are now at the new location). Remove each other location in play from the game.
Choose an investigator to take control of the set-aside The Black Book asset. Shuffle both set-aside copies of Strange Geometry into the encounter deck.