There’s something about the young girls in BioShock. With yellow, glowing eyes and weirdly distorted voices, they are creepier and more disturbing than any monster. The same girl with normal eyes and a sweet demeanour, however, brings out the parent in all of us. BioShock’s Little Sisters can exhibit both qualities, and they’re a big reason the two games in the franchise have been so successful.

Released on February 9, BioShock 2 (2K; PC, PS3, Xbox 360; rated mature), the sequel to the sleeper hit of 2007, begins in much the same way as the first. In this first-person-shooter game, you find yourself looking through the eyes of a cipher in the underwater city of Rapture. Ten years have passed since the events of the first game, and the ocean has reclaimed even more of the failed utopia.

What you do know is that you’re a Big Daddy, one of the protectors of the Little Sisters who wears a deep-sea-diving suit. As you try to unravel the mystery of your identity and how you’re connected to someone named Eleanor, you’ll learn more about the events—and the people—that brought down the city.

Once again, the story is revealed indirectly. The visuals of the beautiful, crumbling environment echo what Rapture used to be, and the sound of metal creaking under the ocean’s pressure clashes with the ’20s-era music, creating anxiety—this place should be abandoned to the seawater.

Plot details are revealed by the characters you interact with and audio recordings you collect as you explore—diaries from Rapture’s citizens, some of whom you’ll recognize from the first game, most long gone.

One of the reasons BioShock was so revelatory was that its finely tuned gameplay and novel-worthy story were unexpected. That meant high expectations for BioShock 2. Thankfully, the developers haven’t made any drastic changes.

There have been minor adjustments to the game’s design. New enemies include the Brute Splicer, a hulking deformity infused with rage, and the eerie Big Sisters. These, you learn, are former Little Sisters, who have gone insane and are themselves protectors of their younger counterparts. The Big Sisters, who come after you from time to time, are fast and frenetic, while the Big Daddies are slow and lumbering. You learn, though, that there is more than one model of Big Daddy, and your prototype is much faster than the others.

In terms of combat, the biggest difference is the ability to wield a weapon and a plasmid at the same time. You’ll be able to improve your weapons as you progress through the game, adding to clip size and damage. Plasmids, the genetic enhancements you purchase, can now be combined. Charging Cyclone Trap with Incinerate, for example, not only tosses enemies into the air but engulfs them in flames.

Much of the developers’ efforts seems to have been expended on creating characters and a story that are as compelling as those of the first game. They nearly lose control of the plot, though. It’s as if it was designed to be convoluted in an attempt to make it as deep and as meaningful as that of the first game. And while your decisions to spare or eliminate key antagonists supposedly affect the outcome of the game, the only ones that seem to have an impact are those regarding the Little Sisters.

You need to defeat other Big Daddies, but in this game it’s so that you can adopt the Little Sisters they were protecting. You become protector then, as the Little Sister drains corpses of Adam, the currency of genetic modification. Then you either harvest the young girl to gain more Adam or rescue her, which nets you less.

Because you have to actively protect the Little Sisters while they’re plundering dead bodies and ingesting the blood they’ve drawn, you’ll have a much more intense connection to them than in the first BioShock. You’ll find that it’s difficult to contemplate killing them. For my part, after releasing them from their burden of being cannibals and turning them back into regular girls, I watched, wistfully, as they scrambled to safety. I kept hoping they would look back—they never did.