FIREBIRD 3 : A MILLION WORLDS WITH YOU - Harper Collins USA

Ever since she used the Firebird, her parent's invention, to cross through alternate dimensions, Marguerite has been at the center of a cross-dimensional feud. Now she has learned that the evil Triad Corporation plans to destroy hundreds of universes, using their ultimate weapon: another dimension's Marguerite who is wicked, psychologically twisted, and always one step ahead.
Even though her boyfriend Paul has always been at Marguerite's side, the Triad's last attack has left him a changed man, and he may never be the same again. Marguerite alone must stop Triad and prevent the destruction of the multiverse. It's a battle of the Marguerites . . . and only one can win.
In the epic conclusion to the sweeping series that kicked off with A Thousand Pieces of You, fate and family will be questioned, loves will be won and lost, and the multiverse will be forever changed.