After Christabel carries Geraldine into the castle, and they go into her room, Christabel is told to undress.  Even though she knows that it is wrong, she cannot resist.  It is as if she is under a spell.  In the morning Christabel feels that she has sinned.  In the morning, Christabel's father becomes enchanted with Geraldine and proposes a journey to inform her family that she is safe. Geraldine's house is found empty and in ruins, the knight returns to the castle with this information, Geraldine then mysteriously disappears. 

When Christabel and Geraldine enter the castle, the lady Geraldine seems unable to walk across the threshhold, which has been blessed against evil spirits.  Geraldine is seized by pain when she tries to enter and must be helped by Christabel:  "The lady sank, belike tho' pain, and Christabel with might and main lifter her up, a weary weight, over the threshhold of the gate" (lines 124-127). 

A second unnatural occurrence is described two stanzas later in the poem. The dog in her kennel, who is usually good-natured, inexplicably growls in her sleep as Geraldine enters.  The poet wonders, "The mastiff old did not awake, yet she an angry moan did make!  And what can ail the mastiff bitch?  Never 'til now she utter'd yell, beneath the eye of Christabel" (lines 142-146).

These portents foreshadow an inherent evil in the lady Garaldine which the innocent Christabel does not recognize.