Judging by their clothes, Exalt might have accidentally wandered out of The Bureau: XCOM Declassified.

Except in the case of a sitcom gag involving a hilariously awkward two-person costume, covert operatives should generally be of the same species as the enemy if they want to be at all covert. As XCOM: Enemy Unknown is about fighting aliens, and was not filmed in front of a live studio audience, covert operatives never had a place in the earth defense organization—until the human threat was exposed.

The upcoming Enemy Within expansion introduces a "literal enemy within," as Lead Designer Ananda Gupta puts it: a terrorist organization called Exalt with sleeper cells peppered across the globe. The underground group is piggybacking on the alien invasion to seize power from the world's governments, perhaps in hope of becoming the alien puppet government. For us, it means two new mission types against human enemies, and a new strategy layer with a Guess Who-style metagame.

Exalt cells are exposed through intel scans (which cost credits) or when they perform an operation—either a direct attack on XCOM or a propaganda campaign which increases panic. At the outset of my hands-on demo, I discover that Exalt has stolen 376 credits from my coffers, exposing a cell in Egypt. Not much of a take given that their punishment is me violently killing all of them.

Once exposed, an Exalt cell can't operate, but if it isn't infiltrated and destroyed quickly, it will relocate and go back into hiding somewhere else. The first step is to deploy a counter operative, which can can be any soldier except a Heavy, and can only be armed with a pistol. After implanting the agent and letting some time pass, I'm prompted to complete a covert data recovery mission. I could decline and abandon my agent, but I'm not a monster. I'm also not very covert—I'm about to very loudly kill 17 Exalt soldiers.

Exalt reinforcements can include perched snipers.

I put two snipers on my team, because I love snipers, but it feels like a mistake at first. Exalt attacks in big waves, and more grenades and rockets would have created opportunities to splash some damage into groups. Instead, I've got two guys who are good at aiming. But precision is helpful during data recovery missions. It begins with the Encoder, a device across the map which can be hacked by Exalt if they stand within its capture radius for three uncontested turns. Once hacked, the Encoder leads Exalt to the Transmitter. If the Transmitter is captured or destroyed, the mission is over, which means missed shots and irresponsible use of explosives are dangerous.

I'm too timid to save the Encoder—I should have known I'd have a few turns to move across the map before the enemy appeared—but I do manage to wipe out a pack of Exalt soldiers standing in its capture zone, expending one of my two rockets. I fall back to defend the Transmitter, and it looks like I'm in good shape until I'm surrounded by a wave of reinforcements.

I'm terribly outnumbered, but I have two advantages. The first is my operative: In addition to my hand-picked assault team, I can command the counter operative I sent previously. He only has a pistol, but he gets the special ability to hack Exalt comm arrays (if he can get to them), which prevents all Exalt troops from firing during the next turn. When my medic is stuck in the open for a turn while I'm re-positioning her to heal an injured unit, the ability is crucial.

My second advantage is that Exalt's primary goal isn't to wipe out my soldiers. The bad guys' first goal is to reach the capture points, so they'll often give up flanking shots in favor of sprinting toward the Transmitter. They are plenty clever, though, using covering fire on my best sniper and tossing a grenade when I foolishly bunch up three soldiers. Even more frightening are Exalt Heavies—not only can their rockets decimate my entrenched defenders and their cover, a missed shot could take out the Transmitter. Later in the expansion, Exalt Elites will be introduced—I didn't see them, but Gupta teased that the group won't shy away from using genetic modifications.

The new Ghost Grenade stealth-ifies your units.

Near the end of my battle, Exalt units start slipping into the Transmitter capture radius inside the map's central building. I'm just barely holding them back, especially thanks to headshots from my star sniper, who I've backed against a wall. In one harrowing moment, a grenade injures him and destroys his cover, putting an Exalt Heavy in sight, with two other Exalt soldiers standing in the capture point. I can't risk letting the Heavy get a rocket off—never mind that he might turn my sniper to giblets, he might damage the Transmitter—so I ignore the capturing units and take the shot. The sniper is a hero, scoring a hit, but can't finish him off. Miraculously, my second sniper—who's been a bit of a dud the whole battle—hits a low-percent shot from behind a car outside the building and takes the Heavy down. The rest of my troops bring down the capturing units with one turn to go. Safe!

I prefer XCOM's objective missions to the "kill all enemies" missions, and point defense works well. The secondary goal creates more opportunities for clutch moments, heroics, and dramatic sacrifices. The one soldier I lost died to protect the mission, not another soldier, which would have been a tough decision were I playing with my own characters on Ironman mode (no save reloading). I'm also excited for the mystery-solving metagame: After destroying a cell, you'll be given a clue as to which country is harboring the Exalt HQ—e.g. "The HQ is not in Europe"—and after three clues, you can start making accusations. A correct accusation leads to a unique mission to take down Exalt for good, but a false accusation will cause the accused country to withdraw from the XCOM project—it's a dangerous risk, but so is letting Exalt increase panic and interrupt your primary mission.

Along with the already-revealed new locations, mech soldiers, and more , the Exalt subplot gives me confidence that Enemy Within is substantial enough to call me back to world saving duty in November. And Gupta tells me that "even this is not everything" going into the expansion pack. On to the next reveal, then.