Cassie, Sarah, David, and William have survived Camboglanna, but they have one more challenge in front of them before they go home: infiltrate Mordred's castle and free his Brenwyd prisoners. They also must find the Sword of Kings, which is a key part of Mordred's downfall. Overhanging the operation is Arthur's worsening condition and Cassie's worry that they may not have enough time left to re-forge the Sword of Kings, and may not even have enough time left to stay through Arthur's death. Arriving back in their own time, the teens discover that Gwen has been captured by the Brotherhood and scramble to find someone who can fix the Sword of Kings. With the confrontation with Mordred fast approaching, it'll take faith, hope, and a miracle for everything to come together as foretold.