The plot gets moving again when the Enterprise discovers a planet that has something on it with energy signatures similar to Data. The ship races out there so Picard (don't worry we get the Riker "You can't lead an away team" speech), Data and Worf can race around on a dune buggy finding pieces of an earlier model Data named "B4," which some producer's daughter must have thought was cute, but it seems odd because it suggests that the builder knew there would be later models of this robot. Maybe he had gone forward in time and discovered that a future version of himself built later models of Data. Then there is a ridiculous Road Warrior chase scene that ends with the dune buggy making a leap off a cliff into a waiting shuttle that Data maneuvers from the buggy. More than one person in my theatre groaned, "Yeah, right."
The Enterprise is then called to Romulus to meet the new leader of the Romulans because that's what the Romulans requested and Starfleet has yet to smell a trap, so off our crew go. When the crew beams down, Shinzon goes out of his way to frequently hint but never says that he's (get ready) a clone of Picard. It turns out some earlier Romulan Government was going to use the clone to take down the Federation or something. I'm not clear how because it's never explained. However, a new government came into power, squashed the plans, and sent the clone to die on the Planet Remus. Why he wasn't killed immediately is never explained, but obviously those government officials hadn't heard about Oedipus Rex, Snow White or Krzilak Entropus of Rigel VIII. I waited to hear how the Romulans got Picard's DNA in the first place, but this plot point like many others was never explained.
The movie then becomes like ST II: The Wrath of Khan and Shinzon hunts down Picard because Shinzon's molecular structure is accelerated and breaking down and he needs Picard to replenish himself somehow. B4 is a plant and actually under the control of Shinzon, so he assists in the security breaches, which lead to the usual ship-to-ship captures and escapes that we've grown accustomed to.
There is one positive note: the battle scenes are very well done and are the best parts of the movie. It's just a shame that you don't care what happens by the time they occur. My favorite part is seeing the Enterprise crash into Shinzon's ship and you see Remans running through the hangar trying to get away.