They walk — or rather, sit — among us. At any given time there are hundreds of thousands of people playing the multiplayer version of the Call of Duty Black Ops combat game. And you’ll know them from their absence from the rest of the world on Tuesday, February 1.

That’s the day when the hot-selling online warfare game, whose sales racked up $650 million in five days and have already topped a record-setting $1 billion, will get a further boost: The first Black Ops map pack, Call of Duty Black Ops First Strike, will debut exclusively on Microsoft’s Xbox Live online service.

If video games are the new Hollywood, map packs are the new, smarter sequel. Instead of coming years later, though, like rehashed studio fare, these downloadable expansions to existing games keep players addicted to a recently released title.

Here’s what will go down on February 1: Hardcore gamers are likely to converge on Xbox Live and download the map pack for $14.99, or 1,200 Microsoft points.

As proven by last year’s Call of Duty Modern Warfare 2 map packs, the launch of this kind of downloadable content is as huge as a major launch of any other huge blockbuster game. $14.99 may not seem like a lot of dough — a movie ticket doesn’t cost much less these days — but it will likely dent sales of new games.

For the video-game industry, the impact will be obvious. February’s retail sales numbers — which will already be low because of a shortage of Xbox 360 consoles and Kinect motion-control systems — may be weaker than usual since the downloadable map packs are not counted in retail sales figures produced by market researcher NPD.

And for the rest? Even if you don’t play, you’ll feel the impact, from workplace absences to empty beds. As we noted before, spouses of gamers may care about this so they can plan their solo vacations and make sure they don’t plan any romantic holidays around Feb. 1. (Yes, it was nice of Activision Blizzard not to schedule this on Valentines Day). On top of that, they consume the time of hardcore gamers as they extend the value of online play with new multiplayer arenas. A year ago, the two map packs for the previous Call of Duty game, Call of Duty Modern Warfare 2, sold more than 20 million units. That generated roughly $300 million in sales for Activision Blizzard.

What’s in these packs that promises to hold gamers’ attentions? The First Strike maps will include four settings: Discovery, in the Antarctic research station that is a scene in the game; Kowloon, set on the rooftops of the district of Hong Kong; Berlin Wall, featuring a firefight at Checkpoint Charlie, where the Americans and Russians squared off; and Stadium, set in an American hockey rink. It also includes a Zombie map dubbed Ascension.

Kowloon looks cool with a “zip line” you can slide down to move quickly from one end of the map to another. The Discovery map has a snow bridge that can be blown up with a grenade. Berlin Wall has more room for sniping and a “no man’s land” in the middle that is covered by auto-turret machine guns. The Stadium game is a short-range map where tactical insertion, or finding a key point to enter the map, is important. Dan Bunting of developer Treyarch says that users wanted more vertical movement through buildings, more opportunities for long-range sniping, and interactivity.

Clearly, Activision Blizzard planned this map pack in advance. Last year, Call of Duty Modern Warfare 2 sold more than 20 million units. But the first map pack for Call of Duty Modern Warfare 2 wasn’t ready until March 30, or 4.5 months after the first game debuted.

This time, Activision Blizzard is debuting the first map pack for Black Ops just 84 days after the debut of the game itself. I’ll be one of the people downloading the map pack on the first day. I’ve already achieved 50 out of the 50 levels available on multiplayer and am cycling through again, at 20 out of 50 for my second time around. And it hasn’t gotten boring yet. Check out the video preview of the map pack below.