If you would like to write a scenario for this game, you have to consider the three main components of a scenario: victory conditions, NPCs and scenes.
Victory Conditions
This is the core of the scenario. First you have to decide, wether the PCs will fight against each other or for a common goal.
If you would like to write a competitive scenario, victory conditions won't be your main concern. You only have to decide how difficult should it be to win. You have to set a target number wich has to be reached by any of the PCs with all his/her reward values. The first player to reach the target point with all of his/her reward values each, is the winner.
If you would like to write a cooperative scenario, it will be more difficult. The simplest way to create a victory condition is to make up a terrible, dark etc. secret that has to be find out. The nature of the secret mostly generates a situation that can be further explored in the scenario. For example: someone is blackmailing you, who can be it? Or someone is abusing the secretaries in the office you work in. Is it a boss or one of the security guards?
You have to place this secret: Wich core element does it belong to? Who knows about this secret?
If you are writing a cooperative scenario, you should begin creating NPCs around the goal of the game, then make up a timeframe in wich the scenes happen, where the PCs can meet these NPCs.
If you are writing a competitive scenario, you should first make up the scenes wich will be the arenas of the social battles raging among the player. Then create the NPCs wich can be attacked and wich can attack beside the other players.
Creating NPCs
Creating NPCs is very similar to fiction writing. Important is that the NPCs of the same scenario should have some contact or relation with each other. Think logical and think about with whom do the PCs meet. Really fullblown NPCs are only needed if the person is able to some social battling. Most of the people can be made into an NPC, but there is the possibility of creating "innocent bystanders" who can be held as shields etc.
You have to create the automatic strategies of the NPC using components, then make up the secrets known by the NPC. It is important to have unimportant secrets to mislead the players. Be aware, that if the secret posing as the victory condition is too easily accessed, it is possible that the players win accidentally. You don't want that. Don't forget that an NPC can have multiple strategies that are changed from scene to scene.
Creating Scenes
Scenes are what PCs can attend and wich are populated by NPCs. The linked web of scenes creates the sense of story for the players. You have to describe what the NPCs do in such scenes (for example if an NPC attacks the players or not). The scenes determine wich strategy do the NPCs use, not to speak about the mood changes caused by them.
You should create the scenes with the purpose for the PCs to solve the scenario. There are two simple ways to do this: you should mark a deadline, when it will be late and the players have to hurry to solve the problem OR the scenes should be circular. For example a day's job: at the office in the morning, at the cafetaria at midday, at the office again in the afternoon and at the bar in the evening.