More information see: Maelstrom
Daniel, along with Dr. Stephen Shin, is invited to Atlantis to help Arthur figure out why Atlantis is having underwater earthquakes. They soon discover that Atlantis doesn't recognize Arthur as its true king because Atlanna, Arthurs mother isn't dead. Daniel and Shin, work on a solution while Arthur and Mera try to track Atlanna down. They travels lead Daniel to Gorilla City and to the Maelstrom.
While in the Maelstrom, Daniel is attacked by a Fire Troll who breaks his back. He then dies in Arthur's arms, but he dies happy because he saw Atlantis.