I have a suggested plot plan.......
Moeganna appears to Celia and offers a truce of sorts.
The spell at the tower is one of 5 places in London the men in white and/or the man trying to be king has set up a spell pentagram etc. They are using the power of the 5 spells to try to force the Morrigan to bring forth Camelot.
She thinks Celia,owes her. Using her name got you,your way. So if we will find the 5 points of power and,destroy the spell at each, she will be free to,exact revenge on her tormentors/ those who tried to,yet her.
This would,ask be from,the point of, view. The truth might be that she tried to,yet them, hoping that if she helped Arther return then she could,rule,by his side. When they didn't call for,it, she was trapped helping but not,getting her way.
Either way, we break the 5 spell points the two powers fight each other, we get out ok.
The 5 place tower of,london, big Ben, windsor Castle, ?, ?
Any thoughts?