Building on the high level overview in a creative way is where a writer can stretch their writing muscles. This is when the story begins to take real shape, the characters become fully developed, new ones added and where exciting conflict is developed.
This is also where the story objectives and obstacles should be tied into those relating to the gameplay. Developing the detail of the story and plot should never be about the writer going off and concentrating on their own thing, but keeping in constant touch with the design team to ensure both are developed in sync.
The work involved in this step can be both invigorating and daunting. Not only must the story work in its own right, it must work with the game design and must embrace the game’s interactivity. The story should help the game deliver a great experience to the players. The detail added at this stage needs to embrace this completely.
A huge help in keeping track of the story’s growth, particularly if it has branching aspects, is to develop a supporting flow chart. This will enable you to see the shape of the interactive plot you create.
Ideally, a tool would be used that not only enables you to create the flow chart but also runs through it as if you were playing the game. Although not specific flow chart software, Twine can be very useful in many respects. You can see the whole story as a kind of flow chart and play through it to test that your story works.