"The Crown of the Sleeping King" is a Trelawney Thorpe, Spark of the Realm story which appeared in the TPB edition of Girl Genius Volume II: Agatha Heterodyne and the Airship City. As it was drawn by Cheyenne Wright, instead of appearing online on the main Girl Genius site, it was told on Cheyenne Wright's Arcane Times site. Unfortunately, the comic no longer seems to be available on Arcane Times. Hopefully, it will return.
It recounts the ingenious means by which this celebrated British intelligence agent foils the plan of Professor LeMort to steal the legendary crown of King Arthur and use it to enslave the people of Britain through mind control.