Before starting to search for these mementos, refer to this video for a visual aid.
1. As you begin the mission you are on a bridge, the memento is straight in front of you in the middle of the bridge.
2. Before entering the mansion the memento in on the left end of the porch.
3. After running over the clock hands, a split screen view will appear showing you where to go, head that way by wall running to the middle platform and then wall running again, then before entering the new hallway, follow the balcony path around to the room with the memento.
4. In the area that you have to defeat a wave of enemies and then kick the four switches in each corner of the area, go to the side that has the poles sticking out which you can "perch jump" on and from to the platform above, walk around and over the narrow plank which connects you to the platforms which have the memento on the last platform, you can see this memento as soon as you’ve "perch jumped" up the poles.
5. Once your passed the "poison gas" area you will be on the roof, but before going all the way up the stairs go left underneath the arched dragon statue and follow the path around the last memento