Situation

I am making a website which purpose is to sum up (including all spoils) books, video games, series etc ... The goal is for people to catch up with the story if :

• They didn't play the last game for instance and want to know what happened
• They just forgot some details and want to be reminded

Question

As everything is based on these summaries, what is the maximum size that a user could bear to read ? It has to be complete but short enough for the user in order not to be discouraged. Is there any known study on the topic ?