I have an idea.
The setting is on a UN exploration ship in the 2500 century or something. During the last jump to hyperspace, the ship was transported in a split second to a pocket dimension within hyperspace, due to the incomprehensible physics of the hyperspace. Within this pocket dimension, the ship woke a slumbering entity. This entity had interrest in realspace, and when this ship shows up, it emidiatly begins to examine it. Even thought the ship only existed there for a split second, it was enough. The entity was alarmed of what it found. The race it found within it, the humans, had a soul simillar to its own. They even had such psychic potential that they could eventually threaten its existence. However, if it could enter realspace again, it would be able to consume this soulbearing race long before they even became aware the entity's existence. It figured out that it could possess the ship and use it as a vessel to realspace, however, the time it had to do that was too short to do such a complicated thing. Instead, it decided to meld a piece of its soul together with some of the crewmembers', have them to kill the rest of the crew when the ship was back in realspace, and then jump back to the pocket dimension.
However, unknown for the entity, the souls of the human crew did their own examination of the entity. When the ship was safely back in realspace, everybody knew what had happened, but they did not know who who was infected by the entity. Now a fight will begin on this ship, a fight that will decide if humanity will be extinguished or not.
The roles I thought of was these:
Guardian (Guardian Angel)
Security Officer (Crazy War Veteran)
In this future, humanity has discovered their psychic potential and has begun to develop it. Psychics are used in all aspects of the human society. Psychics are often given jobs that fits their gifts.
The Crewmembers come from nearly every corner of the vast UN empire. Most of them come from Sol though.
The Infected can no longer be considered human, and thus are no longer protected by the Human Rights. Even though they do have human needs and emotions, they ignore them and will do anything to release the Entity. They must be tortured and killed no matter the cost.
The Telepath works as the ship psychologist, and uses his/her telepathic abilities to see what's going on in the pasient's mind. Now as these infected suddenly shows up, it becomes clear for the telepath how important role he/she will play.
The Guardian possess an obscure psychic power. Through means still unknown the Guardian can actually manipulate the universe to change the outcome of an event. This power only works when it saves the life of another.
The Empath can sense persons' emotions and manipulate them, he/she can even create bonds between persons that are much stronger than love. The Empaths are often used to check the morale of the crew.
The Security Officer is an old veteran from the Mars War. He/she would normally do anything to protect his/her crew, but now as the enemy is hidden among the persons he/she was to protect, he/she is put in a very strained position. He/she is most likely to take somebody down with him if he's lynched.
Haven't thought up a background for the Aer, sadly.