You need to give the final tablet to Sparky and free him from his shackles. Doing so will award the player with the ability to upgrade items and socket runes into their gear from any Vestige. You can read more on the location of the Rune Tablets in this guide here.

• Tablet 1 - Fitzroy Gorge Cave.
• Tablet 2 - Mining District building before the Skien.
• Tablet 3 - Tower of Penance.