When playing as Dr. Lindsey, find the two Runes for Summon and Creature. One is found in a zombie on the staircase down on the last floor and another is on the last floor in some cobwebs. Use your archeological brush to uncover it. Combine these two runes together to make the Summon Trapper spell. Go back up to the floor with the gold statue and find your way to the machinery that was uncovered when you dispelled all the magick fields. When you examine it, you will learn that there is a hole small enough for a small dog to walk through. Summon a Trapper to walk through the hole. Inside will be a bridge with two Horrors on each side. Walk past them and onto a switch with a purple Rune on it. Press A to kill the Trapper and take control of Lindsey again. The switch will have opened a door behind you, where the Mantorok Rune is located.