ANemesis refers to an enemy or an opponent that seems unbeatable. More specifically, it is an arch enemy with whom the protagonist (often) has a long-standing rivalry for very personal reasons. In the context of the movie, Shinzon appears to be Picard's nemesis, due to Shinzon's frustration of feeling like an inferior version of Picard.
AWith no warp drive, no photon torpedoes left, and the Romulan warbird 'dead in the water', it is up to the Enterprise to defend herself against the Scimitar. Shinzon positions the Scimitar directly in front of the Enterprise, and, knowing they have no weapons left, suggests they surrender. Picard suddenly rams the Enterprise into the Scimitar, seriously damaging and disabling both ships, but not the Scimitar's thalaron weapon. With no other option, Picard tries to initiate the self-destruct sequence but finds that it's offline due to the damage. As the Scimitar backs itself away from the Enterprise, Shinzon orders the deployment of the thalaron weapon, intending to kill everyone on the Enterprise. When Picard realizes Shinzon's intent, he places Data in command and beams over to the Scimitar, after which the transporter blows up. Realizing that Picard now has no way to get off the Scimitar, Data leaps across the airless void between the two ships and sets out to find Picard, who is already engaged in hand-to-hand combat with Shinzon. With two minutes left until the thalaron firing sequence begins, Picard lures Shinzon into a lunging attack and kills him by impaling him onto a metal support rod. With less than 30 seconds left until the thalaron weapon fires, Data locates Picard and plants his single-use personal transporter on Picard. The Captain safely beams back to the Enterprise, while Data blows up the thalaron device, taking both the Scimitar and Data with it. Romulan commander dispatches rescue ships and invites the Federation to resume peace talks. Picard and the senior staff retire to the Captain's room, where they have a tearful salute in Data's honor, and reminisce about their adventures with him. In the final scene, as the Enterprise undergoes repair in space dock, Picard says goodbye to Captain Riker who is preparing to leave the Enterprise in order to take command of the USS Titan and begin peace talk with the Romulans. Picard then meets with B-4 to tell him about his 'brother' and how Data's curiosity led him to strive to improve himself. B-4 doesn't quite understand but, he is seen trying to sing 'Blue Skies'.
AStar Trek: Nemesis is set after Star Trek: Voyager. After Voyager finally returned home to Earth, Captain Kathryn Janeway was promoted to Admiral and she gave Captain Picard the assignment of going to Romulus and meet with Shinzon.
