Dark Mirror " The ultimate terror lies within . . . " Dark Mirror is a Pocket TNG novel written by Diane Duane . Published by Pocket Books , it was first released in hardback in . Summary . While on a scientific mission at the edge of the Milky Way Galaxy – where the phrase " empty space " can be taken quite literally – the rendezvous with a ship from the nomadic Lailaru race , with whom a researcher from Starfleet has hitched a ride after a long research mission . The researcher , Commander " Hwii " , has been studying hyperstrings – intangible connections between celestial bodies that seem to tie them together , and provide a sort of invisible " map " to the galaxy . Shortly after the rendezvous , the " Enterprise " experiences a strange disturbance , and Hwii panics , insisting that his sense of direction tells them they are " not in the right place " despite the fact that their stellar position appears to be the same . The crew realizes what Hwii is talking about when an intruder is discovered tampering with the ship ' s computer core , a Lieutenant named Mark Stewart , who is an exact doppleganger for another " Enterprise " crewman . Research into historical files lets the crew realize that the ship has been pulled into another universe , one that was first encountered by the crew of the original " Enterprise " a century earlier . Except , while that earlier crossover was an accident , this time the effect seems to have been produced on purpose . The " Enterprise " ' s long - range sensors detect their counterpart : the " ISS Enterprise " - D . The ship carefully maintains its distance , while trying to determine the best way back home . Eventually Picard ' s crew decides that the only way is to infiltrate the Imperial vessel and examine whatever apparatus they used to cause the transfer . La Forge and Troi are selected to carry out the mission – La Forge because of his computer skills , Troi because her counterpart ' s position as the ship ' s " security officer " would allow them unfettered access . However , the away team soon runs into difficulties which require that Picard join them aboard the Imperial vessel . After Troi and La Forge incapacitate Picard ' s counterpart , and stash him in a closet aboard his quarters , they take refuge in an engineering crawlspace while Picard has to spend a day as " himself " aboard the Imperial vessel . It is a harrowing experience : Picard gleans that the ISS " Enterprise " is waiting for an opportunity to pounce on its " primary universe " counterpart . On an " inspection " tour of engineering , Picard realizes that the Imperials ' plan is to capture the vessel intact , then massacre its crew and return to the primary universe , masquerading as their counterparts . After a few months of gathering all necessary intelligence on Starfleet ' s dispositions and defenses , the Empire will invade , challenging the Federation , Klingons , and Romulans on multiple fronts – the mirror universe Starfleet projects that they may be able to conquer the entire quadrant in as little as a year . While La Forge and Troi continue their attempts to penetrate the Imperial vessel ' s computers , Picard decides he needs to slow them down with a little sabotage of his own . He takes a handful of surgical nanite s borrowed from Beverly Crusher , reprograms them with sabotage instructions , and slips them into the ship ' s systems . Within an hour , its systems are crashing , leaving it dead in the water . Troi and Picard also incapacitate La Forge ' s counterpart , and Picard orders " La Forge " to get to work repairing the ship , allowing La Forge to access the computers . Unfortunately , La Forge is betrayed by one of his assistants , and tortured by Security Officer Troi in the agony booth , where he breaks just enough to allow Troi to realize who " Picard " really is . Picard rushes to his counterpart ' s cabin just as the other Picard is regaining consciousness . The two fight , and Picard - prime knocks mirror - Picard out just as Troi ' s guards storm into the room , killing Barclay in the process . Picard is so enraged at this senseless murder that he forgets his cover and vents that rage full - bore at Troi – an emotional overload that shocks her . Mistaking the unconscious Picard for the primary universe imposter , Troi weakly orders it taken to the booth , then quickly retreats . During the confrontation with Troi , Picard is discomfited to realize that that universe ' s Worf has realized who he really is . Worf does not speak up , however , and he says he will help Picard and his crew escape – a small return for the momentary kindness Picard showed him while acting as the ship ' s captain . Troi , acting as her counterpart , has La Forge released from the torture chambers , and they rendezvous with Picard . Before they flee the Imperial ship , Picard repeats the advice given by James T . Kirk to a hundred years earlier : that the Empire ' s eventual collapse is inevitable , and now , with the Empire grasping at straws to find " new worlds to conquer " , that collapse is closer than ever . Picard urges Worf to spread the word in secret among his people , and the Empire ' s other subjects , to be ready to rise up when the moment presents itself . Worf , presented with the first ray of hope he has ever known in his life , thanks them and wishes them well . Troi stuns him to cover up his complicity , and all three of them beam back to their shuttle craft , and from there back to the " Enterprise " . With the information stolen by La Forge , the " Enterprise " crew is able to duplicate the " switchback " device the Imperials used , which allows them not only to return to their own universe , but to " snap back " the ISS " Enterprise " when it tries to follow them . During the debriefing , La Forge reports that , in escaping from the Imperials , they have perfected a " snap back " method that can be widely distributed throughout the Federation , to repel any Imperial vessels that try to slip through or invade in other parts of the galaxy – the Imperials were so enamored of their new technology that they decided to use it before developing a countermeasure to the " snap back " technique . Relieved to be " home " at last , the crew releases much of its pent - up tension with an impromptu opera performance in one of the ship ' s holodeck s . After a thoroughly enjoyable evening , Picard leaves with Crusher on his arm , as he reflects that the mirror universe , however morally inverted it was , still had decent people like Worf inhabiting it , and he wonders aloud whether a man really can change the future with just a few words . Crusher kisses him goodnight and says that , in their universe at least , the single word " engage " seems to work wonders . History of the mirror universe . The Terran Empire . The Terran Empire ( called " United Empire of Planets " here ) was formed from the ashes of the Eugenics Wars , where Khan Noonien Singh and his Augment followers were not defeated as in the primary universe , but instead established competing empires that eventually wiped each other out in nuclear holocaust , using atomic weapons delivered by ion - powered craft . The surviving governments eventually banded together to form the Empire of Earth , and began expanding into space , fixated on assuring the survival of their own race . In the mirror universe , there was no World War III , a cataclysmic event that convinced the primary universe ' s Earth population to band together for peaceful purposes . However , Jean - Luc Picard , examining his counterpart ' s collection of literature , finds evidence that the " moral inversion " which differentiates this universe was not born out of any single turning point or event , but rather built up gradually over thousands of years , beginning some time around that of the Ancient Greeks ( Picard notes that Homer ' s " Iliad " is roughly similar to the version he is familiar with , but after that the moral inversion follows swiftly ) . After terraforming Mars with a casual indifference ( wiping out numerous artifacts and fossils in the process ) , the Terrans then , with the development of warp drive , expanded out into interstellar space , solely intent on conquest . Alpha Centauri – already inhabited by colonists from another local system – was " cleansed " and re - colonized , as was its foster planet , Gamma Centauri . , having never been grown past its violent roots through the teachings of Surak , became a valued ally of the Terrans . Eventually , contact was made with the Romulan s , leading to a war every bit as bloody as it was in the primary universe . After the Romulans were defeated at the Battle of Cheron , the Terrans invaded the Empire itself , destroyed Remus , and demanded the surrender of Romulus . The Romulan people committed collective suicide rather than surrender , and the Empire took over the planet . Not long after , the United Empire of Planets was formed , and continued to expand . As narrated by Worf ' s counterpart , when the Terran and Klingon Empire s clashed , the Terrans were eventually victorious , after another protracted and bloody conflict . Unlike the Romulans , the Klingons chose to live , and the Terrans discommendated them , " en masse " , and reduced them to serve as slaves . Jean - Luc Picard remarks on the irony that the mirror universe ' s inhabitants have never encountered Q or the Borg , the only powers he can think of that might actually have outmatched and humbled them . By the late 24th century , the Empire encompasses the entirety of the galaxy ' s Sagittarius Arm . Because the Sagittarius arm has become disconnected from the rest of that universe ' s Milky Way galaxy by everything but gravity , they have run out of viable systems to conquer . Now , there are no inhabitable worlds beyond the Empire ' s borders that can be reached in less than ten to twenty years , even at high warp speeds – hence the impetus to find a way to invade the primary universe . Aftermath of . did more than " consider " Kirk ' s parting message . With the use of Kirk ' s Tantalus field , he became a powerful and influential figure in Starfleet Command and attempted to reform the Empire from within , but was ultimately unsuccessful . He was framed on treason charges and executed , some twelve years after the original " crossover " incident . His father , Sarek , was likewise assassinated a short time later . Before escaping the ISS " Enterprise " - D , Picard tells Worf ' s counterpart that Spock had predicted the Empire would collapse in approximately two hundred years ; in their time , one hundred of those years had already passed , and the Empire was closer to collapse than even Spock anticipated . Picard encouraged Worf to spread the word among his people , to be ready to rise and retake their freedom and their honor when the chance came . The ISS " Enterprise " and its operational history . In the mirror universe , the ISS " Enterprise " ( ICC - 1701 - D ) is similar in appearance to its counterpart , but displays marked differences : In summary , Picard finds it " a cruel look , and intimidating " ( p . 62 ) . The Imperial ship ' s engine power and weaponry is also significantly greater : more powerful phaser bank s , a complement of photon torpedo es six times greater than the USS " Enterprise " carries ; more powerful deflector shield s , and several different varieties of weapons not equipped on Federation vessels : " nova devices " , " molecular disassociators " ( described as an improvement on a weapon first developed by the Romulans , possibly an early variant of the disruptor ) , and " atomics in several different flavors . " The reason for the last item on the list is not given , but the Empire may have decided that the relatively low power of these weapons was an acceptable loss given that , unlike photon torpedo es , they wouldn ' t compete with the engines for antimatter . It is only notably inferior to its counterpart in terms of sensor capability , Worf reflecting that , like the Klingon warriors of old , they have focused so heavily on offensive capability that their ship ' s ability to observe in secret is notably hampered , allowing USS " Enterprise " to briefly monitor ISS " Enterprise " without them knowing . Similar to Kirk aboard the mirror " Enterprise " , Jean - Luc Picard asks for an operational history of his counterpart , and is revolted to hear an " inverted " version of the " Enterprise " ' s early missions ( as chronicled in the first season of TNG ) :