The fiction of FEAR 3, the concept of killer and victim teaming up to confront something horrific, is thick with potential. But when you cede both of those roles to the control of gamers can that tension still exist?

Played alone, FEAR 3 has gamers taking on the role of Point Man, a super soldier psychically linked to Paxton Fettel, the younger brother he killed by shooting him in the head. Both are the sons of powerfully disturbed, powerfully psychic Alma.

While the game can be played completely as a single player title, it also has the ability to be played with a second gamer. The cooperative play through doesn't allow another gamer to drop in at any given moment, instead players have to decide to play as a team at the start of a section.

In the single-player campaign, Fettel is never physically present, instead he remains a constant, mocking voice in Point Man's head. But played with a second gamer, Fettel enters the game as his own, powerful character. He can psychically stun enemies, levitate them and even possess them.

The trick is creating a game that can be played cooperatively by gamers taking on the roles of characters who are meant to be naturally antagonistic to one another. Developers Day 1 Studios call it divergent co-op.

"You have this character who is someone you killed in the first game but is now back with you in this partnership," said Heinz Schüler, art director at Day 1. "You're not clear on their motivations and we're exploiting that grey area in the game.

"While the experience of single player is the traditional FEAR experience, the cooperative experience definitely takes the game into new territories. It's a different flavor of fear."

For instance, players don't have to stick together when playing through the game. There are plenty of opportunities to go separate ways. In those moments, when the players are apart, you never really know if what you are hearing and seeing in the distance is coming from an enemy or your brother.

"One of the things we wanted to focus on was maintaining that sense of dread," said Parker Hamilton, lead system designer on the game. "You're playing as Point Man and your partner is doing other things on the other side of the map and you're never sure if it's your partner or an enemy. It creates these frightening circumstances that emerge out of play."

The addition of a playable Fettel gives players not only a very different way to play through FEAR 3, but also creates plenty of potential for bloody teamwork through cooperative play.

Fettel's abilities are often augmented by Point Man's. For instance he can pull an enemy off his feet, floating him in the air as an easy target for Point Man. Fettle can psychically shield his brother, and Point Man can heal both himself an Fettle.

But the developers wanted to get across that feeling of an uneasy relationship in the cooperative play as well, so they added scoring.

While Hamilton didn't want to go into too much detail about the two-player scoring system, he did say that it will lead to players fighting to see who can get the highest score, the most kills.

That, in turn, can lead to situations where the two brothers, as controlled by two gamers, are deciding whether to help or hurt one another in the thick of combat.

For instance, Hamilton explained, a player controlling Point Man might kill an enemy Fettle is trying to possess to prevent the other player from getting those kills.

"The game is highly influenced by tracking your score and how successfully you're playing competitively and cooperatively," he said. "As you play you will be seeking out a high score."

"There is a very robust scoring system that will impact the decisions a player makes. It's really our focus in terms of trying to increase the re-playability of our game."

Using a scoring system to provoke players to behave as the characters they control would in the game world is a clever approach to a tricky problem. And using that uneasy alliance to augment the suspense, the sense of confusion and dread is a neat trick, that if carried out, could add a new a fascinating direction to the game.