When I got a chance to check out “Mass Effect 2’s” new downloadable content pack, “Kasumi’s Stolen Memory,” at March’s Game Developers Conference in San Francisco, I was pretty excited about what was billed as game’s first piece of paid downloadable content. But after BioWare’s Casey Hudson walked us journalists through the game’s core mission, one detail left me scratching my head.

“Kasumi’s Stolen Memory,” which was set to go on sale today for $7 but has apparently hit a snag, introduces the game’s 12th (and final, according to Hudson) squadmate, a thief named Kasumi.

At GDC, Hudson took us through the bulk of the mission, which is supposed to take about 90 minutes to complete, but Hudson explained that we were getting more than just a new mission. Because the DLC adds Kasumi as a squadmate, other dialogue from her is sprinkled throughout the rest of the game. (You can play the Kasumi missions at any point in the game once you’ve acquired your ship and crew.)

“Kasumi’s Stolen Memory” begins with you meeting the titular criminal on the Citadel, the massive space station that serves as a jumping-off point for many of the “Mass Effect” universe’s storylines. Like every other potential squadmate in “Mass Effect 2,” Kasumi has a mission you can undertake to gain her loyalty, and that lies at the heart of this new chapter.

After recruiting and talking briefly with Kasumi, you learn that she used to have a partner, who was killed by a dangerous criminal mastermind named Donovan Hock. Hock, however, has a memory chip that Kasumi’s partner was carrying, and she wants it back. This, is where Shepard comes in, in a chapter Hudson likened to classic, “James Bond-style infiltration.” You’ll travel with Kasumi to the Bekenstein system to Hock’s hideout, where he’s throwing a party for “a couple dozen of the worst liars, cheaters and mass murderers you’ll ever want to meet.” Once there, you’ll trade Shepard’s usual arsenal for an alias (Solomon Gunn) and formalwear. (You get to keep your pistol.)

Your job is to gain entry to the party and, once inside, schmooze via the game’s dialogue trees to figure out where Hock is keeping the memory chip. I won’t spoil any other details of the mission other than to say that the whole thing culminates in one of “Mass Effect 2’s” signature firefights, which offers an excellent opportunity to try out Kasumi’s unique, back-stabbing-style attack.

After I watched Hudson show off the bulk of the mission during his half-hour presentation, I was stoked to play it. But I was also struck by the ridiculousness of sending Commander Shepard on a mission such as the one found in “Kasumi’s Stolen Memory.”

Commander Shepard is easily Citadel space’s most famous human, a fact both “Mass Effect” games repeatedly re-establish. In other words, despite all indications to the contrary, Hock’s party must be populated by dunderheaded idiots incapable of recognizing a celebrity using an alias. As if to mock the complete cluelessness of the folks at the elite soiree, Shepard even arrives bearing a gift — a statue of Saren, the villain Shepard vanquished when he saved the universe at the end of the first game. Clearly the people of “Kasumi’s Stolen Memory” are so unastute, they run circles around Clark Kent’s colleagues at the Daily Planet, who despite being reporters never notice the resemblance between their colleague and Superman.

Sending Commander Shepard, paragon of humanity, on an undercover mission to infiltrate a criminal mastermind’s hideout does more than strain credibility. It’s reckless and foolish, like sending former President George W. Bush — armed only with a fake name, some native clothing and an oil painting of Dick Cheney — to infiltrate al-Qaida.

That BioWare, whose games are generally known for their excellent writing and inventive scenarios, would commit such an oversight is particularly puzzling. It’s possible, but unlikely, that this disconnect is handled better in the DLC than it was in the presentation. In any case, I’ll still be picking up “Kasumi’s Stolen Memory.” Other than this head-scratching plot point, everything else I saw looked to be up to BioWare’s usual high standards. Plus, stabbing people in the back is fun.