Heart of Mystery is the last puzzle from the Secrets of Creation chain you will do in Pathfinder: Wrath of the Righteous so here are all the tools you need to complete it.
Some puzzles are merely challenging brain teasers but Pathfinder: Wrath of the Righteous sometimes throws another challenge at the players. In the case of Heart of Mystery, the additional challenge consists of an extremely resilient Vavakia that's accompanied by a Balor and a few other annoyances.
Container, not slab, location for Heart of Mystery
You can find the components to solve the Heart of Mystery puzzle in Laughing Caves, located just northeast of the Final Veil. If you popped the portals in Heart of Mystery, you can use them to easily reach the location.
The hard part is inside the cave where you will have to kill a Mythic Vavakia with massive AC so if you rely on basic attacks for damage, make sure you bring Attack-boosting buffs. True Seeing is also great, in order to avoid getting ambushed by a particularly powerful Vrolikai behind the Succubus archer.
Once you chew the demons up, loot everything and for the first time in the puzzle chain, it will not be slabs you're grabbing - it will be containers.
Hearty of Mystery solution
When you're done with that, head over to the Heart of Mystery and line up the containers in the order shown in the image below. Make sure the arrow is pointing north on your in-game compass to get the same angle as the one in the picture.
The red space will be taken by a Full Container, the entirely blue one. The reason I didn't insert it in the image is that a portal appears immediately after and conceals the container positions in the middle.