Collapse into one.
At the climax and denouement sections, the two storylines collapse into one.
I need help on "collapse into one" please. Thanks.
2 Answers
I would say Los dos guiones se vuelven a uno or even Los dos guiones acaban siendo sólo uno if the climax is the end of the story.
Thinking about this more, you could use either phrase as long as you say when in the book the convergence happens.
las dos historias convergieron en una sola