So basically, John Connor and Kyle Reese are leading their troops to disable Skynet’s time machine weapon, while different troops in Colorado are taking down Skynet at its core. Unfortunately, they don’t make it in time, and the original terminator is sent back to 1984. So, they decide to send Kyle back to protect Sarah Connor, but as he’s going back, Matt Smith grabs John and he’s all “you thought it would be that easy?” And Matt’s hand glows, indicating that he’s a spooky scary terminator. So as Kyle’s going back to 1984, he has these visions of Sarah telling him something about moving in a straight line and someone telling him to remember that Genisys is Skynet, but we don’t even know what Genisys is yet. So anyway, the original Arnold terminator is destroyed by the older Arnold terminator, with the help of Sarah herself. Kyle steals a homeless man’s pants and is attacked by a T-1000 without anything ever really explaining how it got there. He saves a cop’s life and rides off with Sarah, but then he tries to attack older Arnold, who Sarah calls “Pops”, and so Pops knocks him out and they drag him to their base. It turns out that Pops was sent back to when Sarah was a kid and that Sarah’s father told her the straight line thing and that Pops raised Sarah to fight the terminators. So Sarah wants to go to 1997 to prevent Judgement Day but for some reason, Kyle knows that the vision he saw was in 2017, and since Genisys is Skynet, that means that Judgement Day was somehow shifted forward 20 years. Kyle tells Sarah the straight line thing and apparently that’s all the convincing she needs, so they go to 2017, just a day before Genisys launches, and they wind up in the middle of a highway naked and are taken into police custody, who are convinced that they were trying to set off a bomb. Arnold got stuck in traffic and couldn’t be there in time, but lucky for them, the cop that they saved in the ’80s is still there and he’s JK Simmons now, and he believes Sarah and Kyle, but nobody believes him. But then John shows up and saves the day and takes them out into the parking garage. Also, it turns out that Genisys is a network that connects every electronic device in the world, and it’s made by Cyberdyne. It also turns out that Kyle is John’s father and Kyle gets all upset that no one told him. So then Pops shows up and immediately shoots John, and Kyle takes it to mean that it was Pops’ plan all along, but it actually turns out that Matt Smith injected nanobots into John that turned him into a terminator and then sent him back in time to create Genisys. So they make it to the Cyberdyne compound but John is following close behind and somehow the countdown to Genisys advances from 13 hours to 15 minutes. Also, it turns out that Genisys is Matt Smith, which doesn’t make a ton of sense because it would mean that Genisys created itself, sort of like how Fry is his own grandfather on Futurama. Anyway, the final battle ends with Sarah shooting John with a gun, which has not worked once the entire movie, but this time Pops shoves his hand through the hole so it can’t regenerate and then holds him down in the time machine, telling Sarah to turn it on even though it’ll tear Pops and John apart. After an extremely touching moment they do it, but Pops survives anyway so none of it matters.
The action is pretty cool.