Showing The Winning Side (Time Hunter) by Lance Parkin

Emily is dead! Killed by an unknown assailant. Honore Lechasseur is called to identify the body, but who should arrive there as well, but Emily! Honore and Emily find themselves caught up in a plot reaching from the future to their past, and with their very existence, not to mention the future of the entire world, at stake, can they unravel the mystery before it's too late?