Lyla of Argus will not let Barry use the power source to power the Speed Force Bazooka as she does not trust Barry and the power source is too dangerous.
Barry wants to break into Argus to get the Dominator power source however its security and defenses make Fort Knox look like a crackerjack box, including a meta human power dampener.
So Barry breaks his no more traveling to the past rule and goes to Siberia in the year 1892 to intercept and recruit Captain Cold from the Legends. The other Legends aren't seen and Barry intends to return Snart to where and when he got him.
KF and Savitar have words about the impending death of Iris, he makes it clear that if she doesn't die then Savitar isn't born. KF reminds him that he has Barry's memories of loving Iris, he responds about how he was created to be disposed of.
Savitar then gets a memory flash as his memories revise and update so that he knows that Barry went to get Snart to get the power source to power the weapon. However he feels he is a god and cannot be stopped.
Love Snart's 4 rules, make the plan, execute the plan, expect it to go off the rails and then throw away the plan.
Wells-19 makes ahumorous attempt to keep the physicist from learning he is the Flash.
Barry finally gets smart asks for Iris to be taken somewhere and for him to NOT be told so that Savitar doesn't know.
They get smart and Wally, Joe and Iris warps to Earth 2, much to Wells 2's apparent surprise.
Note: going to another Earth is smart, but Earth 2 was not. Earth 3 where Jay comes from, or Earth 19 where Gypsy comes from would be better.
Barry disguises as Lyla and starts to infiltrate Argus with Snart. Of course he has to ditch the disguise after decking some guards.
Iris and Joe have a father/daughter moment she then gives him the engagement ring to give to Barry in case she doesn't make it. This explains why she doesn't have the ring on in the death scene.
Grodd is contained in the Argus facility. They also see the cells for the Suicide Squad.
The door to the power source can withstand a 30 megaton blast and a computer lock that cost 10 million.....so Snart has it open in 37 seconds
Then they find that King Shark is guarding the power source.
Barry takes the cold gun and wants to blast King Shark. Snart comes up with the idea to just lower the temperature in the room to knock out KS, or Barry can kill KS. barry returns the gun and Snart starts to lower the temperature.
Wells-19 rather humorously asks the physicist to join Team Flash and they kiss.
Barry takes the power source, the alarms go off and Barry gets out before the door shuts and Snart is stuck in the room. Snart reminds him that sometimes the tough call has to be made. Barry radios for help.
King Shark awakes and Snart tells them that if Cisco saves him he will put in a good word with his sister. They get Snart out and KS is briefly......disarmed. They then get captured by Lyla who tells Barry that she watched the whole thing and that Barry did the right thing by trying to save Snart and gives him the power source.
Barry returns Snart to 1892 and Snart tells Barry to stop beating Savitar at his own game and to be a hero.
At Star Labs, what appears to be the Flash arrives and Wells 19 tells him that Iris is on Earth 2. We then see that it is Savitar dressed as the Flash! He goes to Earth 2 and easily beats Wally then emerges from his suit to face them. Joe tries to reason with him. Iris surrenders and begs him to not kill them. He states they need to see her die before he kills them.
Barry arrives too late to intercept. Wally is down with a broken leg so this explains why he isn't there in the future when Savitar kills Iris.
Barry tells the others to make the plan to use the gun and not tell him and heads out for the encounter.
Cisco gives Wells-19 a pep talk and then gets a vibe of KF intercepting him. Barry tells him to go save Caitlyn and he will go save Iris. This explains why Cisco doesn't seem to be around in the death scene. Wells 19 also looks at the piece of Savitar's armor.
Barry arrives at the scene at the appointed time.
Cisco goes to face KF.
Barry hits him with the cannon but it doesn't work. Turns out Savitar has the philosopher stone which shields him from the gun. The stone is solidified speed force.
Barry runs at Savitar and we see that Iris recorded her making wedding vows to Barry in a recording she left behind.
Savitar then skewers Iris and leaves.
Next week should be the season finale, they say it will be a massive cliffhanger.
Also nice tribute to Carmine Infantino in this episode. Similar tributes were done in the 90's series too.