I studied How the image of Count Cagliostro been distorted to fulfil the needs and purpose of numerous historians, rivals and celebrities of the 18th Century. He was a con-artist, magician, religious icon to an extent.. it was so fascinating. i did really well in mine, well by my standards.. i got 38/40.. and i think the only reason why i did so well is because i loved what i did. it wasnt a chore to study, or to read a book about him.. because the work you need to put into a major work is HUGE.. and you need to want to do it! sorry you've probably heard that 20 billion times, but its an obvious point!
but i was in ur boots.. i did anc and modern in yr 11 and i had NO clue as to what i was 'interested' in.. i never really sat down and thought about what i loved so much about history.. so, i went into borders and looked in the history section and just searched until i found out what sounded interesting! its probably not the BEST way to do it, but it was still fun.
i really hope you do well.. just read up and dont waste ur time early on in the year when you're work load isnt too much.. its hell trying to write a major work in the holidays whilst trying to study for trials.. its not a good mix!
best of luck!
p.s. other topics of interest where Olga Chekhova - she was an a Russian film actress and a German spy.. or maybe the other way round.. umm, the princes in the tower, jack the ripper! however, do something original.. not something about King Arthur or about Queen Elizabeth.. do something daring, and fun! and original, so the markers think its cool and they cant compare it to anything else!