This is a recap of Star Trek: Nemesis. See the main page for a list of tropes appearing in this film.
After a nontraditional Title-Only Opening, we zoom in on the fair planet Romulus. It seems the Romulan military has a problem. They support some guy named Shinzon from a planet called Remus and the Romulan Senate doesn't like Shinzon very much. But the military also has a solution to this little quandary. After they leave the Senate chamber, a special effect goes off and kills everyone Professor Quirrell style.
Meanwhile, Riker and Troi are getting married. Sorry, Worf/Troi shippers, it was never going to happen. As it happens, this marriage also coincides with Riker's assignment to serve as Captain of his own ship, the Titan. Troi will be serving with Riker on the Titan while Picard is getting Data as his new First Officer. It's the end of an era, but presumably every time the Enterprise ends up in a mildly interesting situation from now on, it will just happen to be on the day Riker and Troi stopped by for a visit. At least that's the way it works with Worf. Oh, and Wesley is there and wearing a Starfleet uniform despite that whole Traveler business. Anyway, later on the Enterprise, Worf picks up a positronic signature from some planet near the Romulan Neutral Zone. Data surmises that it must be coming from an android. Apparently, the presence of a single android on some random planet is a Big Deal and the the Enterprise sets off on this mission which is clearly worthy of Starfleet's flagship. Arriving at the planet, it's specifically mentioned that it's home to a pre-warp civilization. Who knows why this gets mentioned, considering it will have no impact on the plot and will also create a major Plot Hole. So anyway, Picard, Worf, and Data fly down to the planet to try out some wacky all-terrain vehicle, a mode of transportation which seems considerably less useful than your average shuttlecraft. They find the parts of a Soong-type android which resembles Data, but then they get attacked by some random aliens for no explained reason. A car chase ensues and they return fire with their phasers because, as always, the Prime Directive is optional whenever it's slightly inconvenient. It's not like the whole plot of the previous movie involved Picard risking his life to defend the Prime Directive. Oh, wait.
Back on the Enterprise, the android's head tells them his name is "B-4" and Geordi concludes that he is a prototype of Data. B-4 is somewhat like Data was during the early episodes of Next Generation. The main difference is that while Data was academically intelligent while having a sense of childlike innocence, B-4 just acts like he is mentally retarded. They immediately decide to assemble him. After all, two disassembled Soong androids couldn't possibly both turn out ot be Evil Twins of Data, right? Right? Meanwhile, Picard receives a message from Admiral Janeway. The joke that she must have been Kicked Upstairs is by now rather tired, so we'll instead make the joke that all those Insane Admirals at Starfleet Headquarters noticed she was one of their kind. Yay, originality! Janeway sends Picard on a diplomatic mission to Romulus, explaining that some mysterious Shinzon guy has just taken over as Praetor of the Romulan Star Empire and has requested a Federation envoy. On the way, Data explains that Remus is the sister planet of Romulus. You know, the one that's only been mentioned once, back in the TOS episode "Balance of Terror". It's home to the Remans, a race which the Romulans use for slave labor and, during the Dominion War, Cannon Fodder (they mention this trope by name, incidentally). Of course, this has never been mentioned before either. Oddly, it's been reported that Shinzon is a Reman, but nothing else is known about him. Anyway, Data decides it's a good idea to share all his memories with B-4. He doesn't see any problem with this because he is such a Straw Vulcan and the writers seem to have forgotten about the existence of his emotion chip. You know, the one which had its own subplot three movies ago. They also seem to have forgotten all about Lore, too.
At Romulus, an uber-warship called the Scimitar decloaks and hails the Enterprise. We get our first view of the Remans, who Look Like Orlok. They send transporter coordinates and Picard beams over with Riker, Worf, Data, and Troi. It turns out Shinzon is not a Reman, but a human — a bald human who looks like Tom Hardy. He starts hitting on Troi and helpfully explains that she is The Empath for the benefit of anyone in the audience who isn't a Star Trek fan. Shinzon talks of peace, but he is Obviously Evil and comes off like a first-year student from Evil Overlord School. He hints that he is the same person as Picard, gives them some of his blood, and invites him to dinner. Back on the Enterprise, Crusher tests the blood and, of course, it's a match — Shinzon is a younger clone of Picard. Down on Romulus, Shinzon is bossing the Romulans around, threatening to kill anyone who displeases him, and the usual villain stuff. You know, in case we weren't clear on him being the bad guy. At dinner with Picard, Shinzon explains that he is the product of a Romulan plot to replace Picard with a spy. After the project was abandoned, Shinzon was sent to die in the mines of Remus, but he survived and rallied the Remans to liberate themselves by overthrowing the Romulan government. The movie tries to convince us that he is a Well-Intentioned Extremist despite the fact that the previous scene just showed him acting like a cliché Card-Carrying Villain for no reason. Shinzon insists that he and Picard are Not So Different since they are, after all, literally the same person. Picard is Genre Blind enough to consider that Shinzon might be all right, but he's at least not stupid enough to trust him blindly.
Back on the Enterprise, the crew has discovered that someone is getting information out of the main computer, and that the Scimitar is emitting some ultra-dangerous form of radiation. Meanwhile, Riker and Troi decide this is a great time to have sex with each other. But Shinzon's viceroy has mind powers, and Shinzon wants to have a little fun. So, with his viceroy's help, he invades Troi's mind to literally mind-rape her! You know what? Maybe Shinzon is the bad guy of this movie. Just a hunch. After Shinzon has gotten his jollies, he goes to the Scimitar bridge and beams over B-4, who is, of course, working for him. Shinzon then has Picard beamed over and imprisoned in a thingy. They take some of Picard's blood by force and Shinzon explains that B-4 has given them the information from the Enterprise computer. You see, Shinzon has a bad case of Cloning Blues and for some reason, this makes him want to go to war with the Federation. His reasoning doesn't seem to be entirely coherent and he's clearly got a few screws loose. But after Shinzon leaves the room, B-4 reveals that he's actually Data having pulled a Twin Switch. He knocks out the only Reman guard left in the room and sets Picard free. Data explains that he's given Shinzon false intel on the Federation and that the dangerous radiation they detected is coming from a Weapon of Mass Destruction. Later, Shinzon and his entourage enters the cell to do something with Picard, but finds him gone. Shinzon, of course, orders they kill the Reman guard lying on the floor. He calls the Remans his brothers, but apparently it's in a very tough love sort of way. Picard and Data head for a shuttle bay and encounter resistance from Reman guards who can't shoot straight. They board a two-person (how convenient) Space Fighter and escape back to the Enterprise. The second Picard and Data are aboard, Riker orders the ship to warp out of there.
Some Romulan complains to Shinzon on a viewscreen about him not carrying out his evil plan fast enough. Shinzon lectures him about patience, acting like he has some serious Chessmastery going when, in fact, everything he's done is random generic villainy. After they shut off the viewscreen, the Romulans discuss the fact that Shinzon is planning to destroy Earth. The Romulans want the Federation defeated, of course, but they think genocide might be a little too evil for them. Meanwhile, Dr. Crusher has discovered that Shinzon is unstable and not just mentally. He's dying and only Picard's blood can save him. Data interrogates B-4 and it's predictably useless. B-4 doesn't even seem to understand that he was working for Shinzon and Data shuts him off for his own good. Geordi has determined that Shinzon's weapon could be used to destroy a whole planet and Picard realizes that he must be going after Earth, saying "I know how he thinks." Well, that's great. Would you bother enlightening us, Jean-Luc? No? Very well, let's review: Shinzon likes the Remans and hates the Romulans for enslaving them. So what's he going to do? Get revenge against the Romulans? No, that would make sense. He's going to help the Romulans destroy their greatest foe, the Federation. And the Remans, his "brothers" whom he's supposedly doing all this for, will not benefit in the slightest and will get treated like a bunch of disposable followers. Can you say "Motive Decay"? Anyway, the Enterprise is going to be meeting up with the fleet at some place in Federation space. Of course, the Scimitar is cloaked and in pursuit. As they fly through an emerald green nebula, Picard mildly angsts about Shinzon proving that he would be a genocidal madman if only his life had been different. Data tries to make him feel better by pointing out that B-4 is identical to him aside from being stupid and nothing like him at all.
The Scimitar attacks and this is the start of the endless action scene which literally takes up about a third of the movie's running time. After firing at the Enterprise for awhile and disabling her warp drive, Shinzon sends over a hologram of himself to gloat in Picard's face. Picard tries to convince him that he doesn't have to be evil, but Shinzon likes being evil and tells him to shove it. At this point, two Romulan warbirds arrive, siding with the Enterprise against Shinzon. The action resumes and soon enough both Romulan ships have been disabled. Some more stuff happens. Troi uses her powers to get a lock on the Scimitar, Shinzon's viceroy and his boarding party enter the Enterprise to shoot at the spaces between characters who can't die, Riker has a fistfight with the viceroy on some random scaffolding inside a Jefferies tube, and the Scimitar blasts a big hole in the front of the Enterprise's bridge. By now, the Enterprise is pretty much a sitting duck, so Picard decides to ram her into the Scimitar, totaling the bows of both ships. Presumably Guinan is dead now, but no one mentions this. Shinzon breaks the Scimitar free and decides to use his superweapon to kill everyone on the Enterprise. "How can he? He'll kill you," asks, of all people, Troi. "It's not about me anymore," replies Picard, who can apparently read the screenwriter's mind. Picard has himself beamed over to the Scimitar since This Is Something He's Got to Do Himself. Disregarding this, Data goes after him. Picard bursts onto the Scimitar bridge and takes out the Reman guards, who continue to show no sign of having had marksmanship training. A fistfight between Picard and Shinzon ensues, ending with Shinzon getting Impaled with Extreme Prejudice. Just as we're celebrating that idiot being gone, Data runs in, beams Picard back to the Enterprise, and sacrifices himself to destroy the superweapon, completing the rip-off of Wrath of Khan's climax.
Back on the Enterprise, everyone mourns the loss of Data and a Romulan ship offers to render aide. Sometime later in orbit over Earth, Riker's new ship is heading off to open negotiations with the Romulans. Too bad Romulus will get blown up in the next movie anyway. But wait! B-4 still has Data's memories. The movie ends strongly hinting that B-4 will eventually turn into a new Data. Will he? Well, this is the inauspicious end of the saga of Star Trek: The Next Generation, so we'll never know. The Star Trek Expanded Universe says yes, however. The greater mystery is whether this is a good thing. Data was the greatest character in all of Star Trek, but if he was revived it would just be a ripoff of The Search for Spock.