Barry is back in his timeline and happy that he didn’t get to forget all his memories, but right before Reverse Flash left him, he was warned that things wouldn’t be the same and they sure weren’t. Once he walked inside and mentioned Iris it seemed like she had died and it was frown upon to mention her name like bringing bad memories, but we learned later that her and her dad were mad due to hiding her mom’s death.
When Barry goes to the lab and see everyone there something is odd, Cisco seems angry at him, Iris and Mr West don’t talk. He tries to make jokes and be the same Barry that he has always been but gets pushed back. After some time, he later realizes that the change he made in the past has not only affected him but everyone in the world. He goes and talks to Felicity and tells her everything that happened, how he traveled in time to save his mom and living in an alternate world where he started to lose his memories so he had to come back let his mom get kill and now Cisco’s brother is dead, Iris and Joe don’t talk and now he seems to have a partner that he don’t like.
Felicity tells him that he needs to fix things, but while he is doing that “The Rival” from the other time line is on this timeline and is about to get his powers from “The Alchemy”. When Barry goes to the lab he tries to “fix” things by getting everyone together and make peace with each other but fails. Barry then decides to travel back in time and fix what he broke, but in the middle of the time travel he is pulled out by Jay Garrick The Flash. He tells Barry of the consequences if he keeps going back in time changing things, nothing will ever be the same, no matter how much he tries one thing will be off. He makes his mind to not go back in time no more.
Barry goes back to the lab and tells everyone what he did, Cisco is upset at him for not going back in time to save his brother, and tells him he did it for his mom but can’t help his brother. Barry leaves to confront The Rival, and find out a new enemy is in town Dr Alchemy, when Barry seems defeated we see Cisco come in with his new powers saving Barry. Episode ends with Cisco and Barry making peace, but now Barry’s CSI partner is suspecting of him, and from what I can see it seems that this new character may be a new enemy.