Battle of the Bassen Rift
The Battle of the Bassen Rift was an encounter between the USS Enterprise-E, assisted by forces of the Romulan Star Empire, against the Reman warbird Scimitar, which was commanded by Shinzon. Shinzon, allied with the Remans, had recently led a coup against the Romulans, assassinating most of the Romulan Senate and assuming the role of Praetor himself. Shinzon was a clone of Starfleet captain Jean-Luc Picard, and had developed a vendetta against his originator.
The battle itself, fought in 2379, was a fierce engagement between the Scimitar, a unique and heavily armed warbird of Reman design, and the Sovereign class Enterprise-E, which was assisted by two Norexan class warbirds. The battle ended with the defeat of the Scimitar only thanks to sabotage from within the Reman ship itself, and was achieved at great cost in both manpower and equipment.
Prelude
Following the assassination of the Romulan Senate, Shinzon quickly made overtures to the United Federation of Planets, requesting that an envoy be sent for face-to-face meetings on Romulus. The Enterprise-E, being the closest available starship, was sent on the mission.
Shinzon specifically wanted to lure Picard to Romulus, because he required a complete transfusion of Picard's blood in order to survive — because his temporal DNA sequences had not been activated, his cellular structures were slowly breaking down. Shinzon also wanted to learn more about his counterpart and their "shared" identity.
However, the crew of the Enterprise-E soon managed to see through Shinzon's deceptions. They determined that the Scimitar was equipped with a thalaron radiation generator, a type of biogenic weapon that could effectively destroy all life on a starship — or an entire planet — in a matter of moments. Although Shinzon managed to capture Picard, Picard quickly escaped with the assistance of Data, who had masqueraded as B-4. Once Picard and Data were safely aboard, the Enterprise departed Romulus at maximum warp.
The Battle
The Scimitar pursued the Enterprise while cloaked, waiting for the right moment to strike. Shinzon himself continued to deteriorate both physically and mentally. On the Enterprise, Picard and his crew realized that the Scimitar had to be destroyed, lest it continue to threaten the Federation with its massive weaponry and its planet-destroying thalaron weapon. Fortunately, they also realized that Shinzon needed Picard's blood quickly, or he would die — meaning that Shinzon would be forced to attack the Enterprise before launching any other campaign.
The Enterprise was ordered to rendezvous with Task Force Omega near the Bassen Rift, where it would have the support of other starships for protection from Shinzon. However, Shinzon had been planning ahead — when subspace distortions emanating from the Rift began disrupting the Enterprise's communications with Starfleet, the Scimitar quickly launched its attack. Firing while still cloaked, the Scimitar quickly disabled the Enterprise's warp drive and left it stranded, outgunned and unable to call for help. The Enterprise was able to land some hits on the Scimitar by triangulating its weapons fire and by further firing on any shield impacts but the Enterprise's retaliation inflicted minimal damage to Shinzon's ship while the Scimitar was able to severely weaken the Enterprise's dorsal shields.
A brief ceasefire ensued where Shinzon projected a hologram of himself into the ready room where he offered Picard the chance to give himself up so that nobody else on the Enterprise would have to die. Picard refused and the battle was to resume. It looked like all was lost when two Romulan warbirds decloaked but hope returned when Commander Donatra, CO of the IRW Valdore, hailed the Enterprise informing Picard that the Empire considered Shinzon's attacks a matter of internal security and offered to assist in destroying the Scimitar. Together, the three ships managed to score several direct hits on the Reman warship before the Scimitar's superior firepower destroyed one warbird and disabled the other.
On the Enterprise bridge, meanwhile, ship's counselor Deanna Troi offered a means of tracking the Scimitar through its cloaking device — by telepathically contacting the Reman Viceroy (who had previously contacted Troi in the same way) and triangulating his position and disabling the ship's cloaking device.
With several quadrants of the Enterprise's deflector shields failing, Shinzon then ordered that a boarding party be beamed aboard the Enterprise to bring him Picard. However, the Reman troops were quickly pinned down by Enterprise security personnel on a lower deck. The Reman Viceroy, who was leading the boarding party, was ultimately killed in the assault. During the boarding action, the Scimitar fired a spread of photon torpedoes at the Enterprise, destroying the front of the Federation flagship's bridge, causing an explosive decompression, which killed Lieutenant Branson before an emergency force field was erected to seal the hull breach.
With the battle deteriorating into one of sheer attrition, it appeared that the Scimitar would win thanks to its superior weaponry and shielding - the Enterprise had depleted its complement of photon torpedoes and phasers were only operating at 4% while the Scimitar's shields were still running at 70%. However, Picard wryly commented that in his youth, his first evaluation at Starfleet Academy had suggested that he was extremely overconfident — a trait he attributed to Shinzon as well. In order to stop the Scimitar, Picard ordered the Enterprise to ram the enemy ship at full impulse, plowing the two opponents together.
However, although the Enterprise sustained critical damage in the ramming maneuver, the Scimitar remained primarily operational although the ship's disruptors were disabled. In a final act of desperation, Shinzon ordered the activation of the thalaron radiation weapon, and ordered that every living thing on the Enterprise be killed.
Picard ordered himself beamed aboard the Scimitar to stop the weapon from firing. Just after transport, however, the transporters malfunctioned, making it impossible to bring the captain back. Data decided to launch an incredibly daring rescue mission (him being unaffected by the vacuum of space), hurling himself across the gap between the two ships to board the Scimitar as well.
On the Scimitar bridge, Shinzon and Picard had a final confrontation as the seconds counted down towards the firing of the thalaron weapon. Picard managed to kill Shinzon in hand-to-hand combat with barely thirty seconds remaining before weapon fired. At this point, Data arrived on the bridge and beamed Picard away using an emergency transport unit, and firing on the thalaron radiation generator with his phaser, destroying the Scimitar and sacrificing himself to save the 800 men and women aboard the Enterprise.
Aftermath
The battle ultimately brought about a greater understanding between the Federation and the Romulans, as the two former enemies had fought side by side in battle. The valiance with which the Enterprise fought against Shinzon greatly impressed the Romulans, and the Romulans' decision to assist the Enterprise also impressed Starfleet. Commander Worf, a man who harbored deep hatred for the Romulans, even observed that the Romulans had "fought with honor" — very high praise coming from a Klingon.
Following the battle, newly-minted Captain William Riker of the USS Titan led a Starfleet task force to the Romulan border to engage in direct talks for a final peace between the two sides. It was hoped that this development would lead to greater understanding and a new era of peace in the Alpha and Beta Quadrants.