Since we know only the title 'Toliver's Secret Novel', it's all speculation. It could be a story where Toliver has a secret talent for something, like painting or music, that he's kept hidden from the world. The novel might then be about his journey of revealing this talent, the challenges he faces in doing so, and how it changes his relationships. It could also be a more sinister secret, like Toliver being involved in some illegal or unethical activity, and the story would revolve around how he tries to keep it under wraps and what happens when it starts to surface.
It's a bit of both. 'Goon' has roots in real events, but the filmmakers likely took some liberties and fictionalized certain aspects to create a more compelling narrative for the audience.