You say "tie together", so I assume you have several plot lines? At the very least, several characters! I believe that structure is key, so!
What helps me a lot is taking excel (paper works too, but you can delete and move around easier in excel) and write down, each their own column, the characters in your story. Perhaps group them by something if needed, such as affiliation ("the baddies" "the pirates" "the FBI" etc). In the second row, underneath each name, write a short description for each character. (This is your first checkpoint: How did you describe each character? By what they do or are they just fodder? Ex. "the girl who leads the fight" vs. "love interest/the pretty girl")
Now each column represents a character. Going down is the timeline, each row is the same point in time!
Next, for the rows, mark important scenes at the very left (in the right order, it's a timeline!), or what I do, write down the points of the three-act-structure (first plot point, inciting incident, all that jazz).
Now work your way through this grid! It should add up in two dimensions: For each character, what they do, and for each scene, the interactions (time- and content-wise).
This way you can both see the general story, as well as the individual storylines! Why is this good?
You can see if one character is full of gaps, has nothing to do, or is pure filler/fodder material when they're supposed to be important to the story (in which case you delete or revise them). You can see if the actions of each character makes sense: Does what happens in Scene 3 really make Character F do what they do in Scene 4? You can spot new influences: Maybe Scene 4 affects Character E too!
You can also spot new opportunities! Kidnapping might feel like the only thing you could do because you're coming at it from a "what does a villain usually do?" standpoint, but if you have this grid, you can spot things the villain can aim at, and you can see what s/he wants to do and why. In other words, you make the actions make sense in the story!
This is especially useful if you're writing something with largely hidden storylines or characters, like murder mysteries, where the audience doesn't know who the murderer is until the end, but you need to make it add up the whole way. You can write down everything the murderer does, when they do it, and for what reason, and make sure it adds up. What do they do between the murders? Why did they go back to the crime scene? What happened earlier to motivate them? How does the investigation affect them? You have it all there - but the audience won't see it!