Something similar to this.
Okay, so the basic plot structure I want is that there are two parallel timelines, both of them potential futures for our world. These two timelines have become entangled, and now the fabric of their branes are beginning to collide, meaning eventually one or both will either be destroyed or absorbed into the other. Utilizing alien technology (long story), one of these parallel timelines creates a CTC that'll take them back to before the event that triggered the separation to manipulate history in such a way that their timeline becomes more chronologically "certain" and therefore more likely to survive the collision.
What I'm almost "certain" of myself is that this is all absolute bollocks in terms of real quantum mechanics, but I want to make sure it's consistent. Basically, it goes: someone in the original timeline travels back in time for unknown reasons, splitting the universe into two entangled timelines, someone from one of these two timelines travels back in time again to "fix" history so their world survives, the two timelines merge into one (hopefully).
Does this make sense and does anyone with any more insight on time travel have any suggestions to improve it while still maintaining the possibility of there being conflict between two parallel timelines? I feel like if I can just nail down the rules the rest of the story should be easy (without the lingering shadow of logical paradoxes that is).