Intent on saving Merlin, Gwen enters Faerie and succeeds in going back to Merlin's time. Tapping into her former life as Guinevere, she remembers the secret of how to find Merlin's Stone. Gwen manages to rescue Merlin and, thwarting Morgana's attempt to capture the crystal, returns to the 21st century with the crystal to save Karen - with O'Leary in hot pursuit.

As humanity wallows under Morgana's tyranny, Gwen organizes Tasha, Josh, Spencer, Harve, Louise and Katie - all of whom are unaware that the world was ever different - into a resistance. Reluctantly accepting O'Leary's help, Gwen infiltrates Morgana's dungeons to retrieve Merlin's Stone and discovers her way blocked by Reine, Morgana's chief henchman. In a final showdown, Gwen makes the startling revelation that Reine is, in fact, Morgana, who has used the crystal to rejuvenate herself. Gwen leads her friends to victory over Morgana and returns the crystal to Merlin, thereby restoring reality. As Gwen and Karen prepare to move out of Rosen's and find their own apartment, there's one more surprise left for Gwen: the realisation that Patrick O'Leary is her father.