After downloading the DLC, players can get in touch with Kasumi on the Citadel, either in the middle of an ongoing Mass Effect 2 game or after the completion of the main story (lesson learned from Mass Effect 1 DLC!). Once recruited, Shepard aids Kasumi on a secretive mission of recovery, which requires a suave disguise and a run-in with an influential and predictably corrupt art collector. The content, which also provides the "Locust" SMG, a flash-bang grenade loyalty power and a new Achievement, should take about an hour and a half to complete.
BioWare is currently in the midst of "internal discussion" to determine the price of the DLC, but we'll keep you updated as soon as it's finalized. Look for some impressions of "Kasumi's Stolen Memory" coming soon to Joystiq as part of our ongoing GDC coverage. Spoiler: It looks great.