Mystique, book 1: Dead Drop Gorgeous
Brian K. Vaughan2003

Professor Charles Xavier is the head of the X-Men, a group of mutants born with incredible powers they have sworn to the service of a world that fears and hates them.
But for politically sensitive operations, Xavier uses secret agents, from which it is impossible to go back in case of capture or killing.
When one of these agents is killed on a mission, Xavier must use the only woman capable of taking over ... terrorist shapeshifter, Mystique...
(Collects Mystique #1-6)