Complex sentence: Black Widow, the character, along with Peregrine, is sent on a mission to free hostages being held in a Marseille cathedral by Rapido and a group of mercenaries exploiting the panic over the events in Paris in order to steal France's nuclear arsenal.
Split into simpler sentences: Black Widow, Black Widow and Peregrine are sent on a mission to free hostages being held in a Marseille cathedral by Rapido. He and a group of mercenaries are trying to exploit the panic over the events in Paris to steal France's nuclear arsenal.