The Holy Grail of Eris, Vol. 3 (manga)

In her search for clues pertaining to Scarlett Castiel s framing for attempted murder ten years ago, Constance chances upon a mysterious invitation: a masked ball held by the anonymous Earl John Doe. If she wishes to attend, she ll need courage, cunning, and just a dash of wickedness reminiscent of Scarlett herself. Meanwhile, Randolph Ulster of the Royal Security Force is hot on Connie s trail, and if she doesn t wish for her crimes to be exposed, she must negotiate a solution with him fast. The perfect way to settle things is, of course an engagement?!