The 3189 mission to the Verubin Nebula, where Discovery's crew found that the Burn had been caused by a grieving Kelpien named Su'Kal.
Using data from Ni'Var's SB-19 project and from the black boxes of ships lost in the Burn, Michael Burnham traced the disaster to its point of origin, the Verubin Nebula. Hidden within the nebula was a planet rich in dilithium and the wreck of a Kelpien ship, the Khi'eth.
Saru, Dr. Hugh Culber and Adira Tal went aboard the Khi'eth, where they found Su'Kal, a Kelpien born on the ship and left to grow up alone inside a holographic program. The radiation of the nebula had altered him, linking him to the dilithium around him.
When Su'Kal's mother died, his cry of grief had made dilithium across the galaxy go inert at once, causing the Burn. Saru helped Su'Kal face the loss, and later took him to begin a new life on Kaminar. The dilithium planet gave the Federation a vast new supply of fuel, and Discovery began delivering it to worlds cut off since the Burn.