Episode 8 and 9. Kylo Ren completes his training and conversion completely to the dark side after he killed his father, Han Solo. He is named "Darth Lidicus". His goal is to realign the empire and continue his lineage as Darth Vader's Grandson. Which also includes a subplot to overthrow Snoke. Late in Episode 8 before the credits roll, it is revealed who snoke is. Vader.
Rey obviously begins her training with Luke Skywalker after Luke gets a visit from Yoda (Ghost) and Yoda explains to Luke that the dark side is more powerful now than ever before and driven from an unseen force which puts the previous emperor to shame. Throughout the training, Rey finds out she is the half sister of Kylo Ren. Han Solo had an affair, which led to the divorce which will be explained in the movie once the twist begins. However, Snoke, isn't Snoke. Snoke is Vader (As mentioned above - and you can actually see this as you notice the scar marks on the forehead of Snoke and everything resembles Vader when he took his mask off in Return of the Jedi.) Vader was brought back to life by None other than... You guessed it. Darth Plagueis. He never died. He was manipulating the strings the entire time and trying to gain control of the one true family born of the force. Everything else, including the other movies, were just a side attraction as he gained power and influence over them from different vantages.
The movie ends with Plagueis, Vader, and Kylo Ren in a battle for the ultimate control of the sith. Kylo and Plagueis die. Vader, comes full circle, and destroys what's left of the Jedi once and for all.
The end.
