Shadow of the Two Princes

Uncle Richard is kind and caring, isn't he? That's what twins Jemima and Joe Lancelot think, but the two princes imprisoned in the Tower of London aren't so lucky, because their Uncle Richard is very different.
Travelling back in time to the year 1483, the twins undertake a daring mission. Together with friend Charlie and their talking cat Max, they must rescue the princes from certain death at the hands of their wicked uncle - none other than the infamous villain, King Richard III.
Is this a task too far for the young time-travellers? Will their plan succeed, or must they risk their own lives to save the two boys?