A master thief, Kasumi Goto brings a new element to the game with her recruitment mission. Borrowing from espionage movies, Shepard will help her break into the heavily protected vault of a wealthy art "collector" during a party to steal back a data recorder one of her former associates lost. As such, the first part of the mission finds Shepard in formal attire, mingling to case the place and figure out a plan for getting into the vault.
And like so many movies, things quickly go downhill as their cover is blown and weapons drawn. Kasumi has a unique special power that takes advantage of her stealth suit that lets her turn invisible. Use "shadow strike" and she appears right behind the targeted enemy and delivers a powerful blow with her omni tool that, in many cases, will be a one-hit kill. That does leave her, though, potentially exposed to any other bad guys in the area who can get to her before she can cloak to run away. Kasumi is also plenty lethal at range with the new sub machine guns that can be acquired during her mission.
Once added to the game, Kasumi can be played however you like. She can be taken on any of the galactic exploration missions and future downloadable add-ons. She can also be used as part of a new playthrough of the game, which will introduce a few new character interactions over the course of the story. Either way, her recruitment mission adds about an hour and a half of new play time, including battles described by developer BioWare as some of the heaviest they've put into the sci-fi shooter-RPG yet.