After the destruction of Alderaan at the hands of the Death Star, Commodore Rae Sloane of the Imperial Star Destroyer Vigilance assigns the TIE fighter pilots of Helix Squadron to hunt down any surviving Alderaanians, beginning with investigating the possible presence of diaspora at the Fostar Haven trade station. Helix Squadron leader Captain Lindon Javes debriefs the mission to his men, including his pupil Lieutenant Terisa Kerrill, but privately expresses conflict over eliminating refugees, further complicated when the determined Kerrill reminds him that he taught her to see past the idea that these rebel sympathizers are "innocent".
Upon arriving at the station, Helix Squadron scans the present ships for refugees, to the objections of the stationmaster and his customers. Their investigation is halted by attacks from the station's turrets and the arrival of X-Wings, confirming their suspicions, and Javes heads into the station's tunnels to search for further ships while Kerrill and her squadmate wipe the floor with the rebels. However, upon attempting to rendezvous with their squad leader, the two pilots have their ships disabled by ion missiles courtesy of Javes, who reveals his intention to defect to the Rebel Alliance out of disgust at the Empire's willingness to destroy worlds and attack innocent refugees. As the duo pursue their former commander through the tunnels, a group of X-wings belonging to Rebel unit Echo Squadron is sent to back up the convoy, with one pilot assisting Javes in destroying the Vigilance's targeting system, preventing the Imperials from being able to pursue the convoy.
Four years later, after the Battle of Endor, Javes has ascended in the ranks of the New Republic Navy to the rank of commander and is assigned by Fleet Intelligence officer Ardo Barodai to the Temperance. His job is to lead Vanguard Squadron in ensuring the secrecy of Project Starhawk, a starship project that may be the key to winning the war with the remnants of the Galactic Empire. He accepts, and personally requests the services of a certain Echo Squadron pilot whom he owes his successful defection at Fostar Haven to. Originally offered a cushy position over Chandrila, the pilot takes up Javes' offer and is assigned to Temparance's Vanguard Squadron as Vanguard-5, joining the Mimbanese 'Gunny', the Trandoshan 'Frisk', the Mirialan Keo, and a member of the Sienar clan named Grace.
For their first missions, the newly acquainted Vanguard Squadron are tasked with destroying Imperial ships jamming New Republic communications, before joining the famous Wedge Antilles in capturing a Star Destroyer above Yavin Prime for the sake of Project Starhawk. After foiling an attempt by the Empire to recapture the Star Destroyer, Vanguard Squadron are directed to travel to the Nadari Dockyards on the edge of the Ringali Nebula, where they discover Project Starhawk to be the construction of a battleship using parts from captured Star Destroyers.
But just as four years has rewarded Javes's defection, they have also fuelled a fire of anger, hatred, and fury within Kerrill, now recalled and put in charge of the Star Destroyer Overseer after being reassigned to a boring who-knows-how-many days in the Meram Sector. Her squadmate (who also got treated to the same kind of boredom in the Outer Rim) shares that Dark Side-worthy fire, and joins former ParSec police officer Varko Grey, Imperial loyalist Rella Sol, the close-to-Vader-in-cybernetic enhancements Shen, and Rebel-hater Havina Vonreg (whose last name bears a seemingly striking resemblance to a First Order pilot) as a member of Overseer's Titan Squadron. Sloane, now an Admiral within the Imperial Navy, tasks Kerrill with putting an end to both Lindon and Project Starhawk, reasoning that her past with Javes makes her the ideal foe for him.
Titan Squadron begin their assignment by assisting in the retrieval of an Imperial spy with intelligence on Project Starhawk from a space station above Hosnian Prime, before following a New Republic engineer convoy in the hope of discovering the location of their enemies' project. What was supposed to be a simple Stalking Mission goes awry however when a Star Destroyer under the command of one Captain Amos attacks the convoy, forcing Titan Squadron to intervene in order to keep their lead from being destroyed. The Imperials under Kerrill manage to retrieve data from the convoy denoting the sector where Project Starhawk is located, but Amos is killed and his Star Destroyer is lost; in response, Kerrill has the convoy destroyed to send a message to her former commanding officer, allowing him to realize just who he's got working against him.
As part of a plan to stop Kerrill, Javes sends a message with fake intelligence knowing the Imperials will intercept it, with Vanguard Squadron attacking and destroying the Imperial listening post that picks it up in order to sell the ruse. The message claims Vanguard Squadron are protecting a shipment of magnite crystals vital to the completion of the Starhawk as it travels through a highly volatile area of space known as the Zavian Abyss; in reality, the Starhawk has already been completed, and the supposed shipment is just a dummy convoy consisting of empty, auto-piloted starships. As predicted, Kerrill and the Overseer attack the fake convoy, with Vanguard Squadron fending off her TIE fighters and bombers long enough for it to reach the Starhawk's hiding place, at which point the Starhawk attacks the Overseer with a tractor beam powerful enough to drag it through the Abyss and cause severe damage to it. The Star Destroyer manages to pull off a hyperspace jump, though it and Kerrill are undersandably considered beaten after the beating taken by the latter.
Kerrill, the battered Overseer and Titan Squadron - who had been held in reserve till the very end of the Zavian Abyss battle and were subsequently able to escape unharmed - end up within the Outer Rim's Remitik system. They manage to make contact with an Imperial munitions depot in the area, but find themselves press-ganged into the service of the depot's commander, Colonel Gralm, who's currently dealing with rebel forces of his own. With little other choice, they protect the depot from a rebel attack, while taking advantage of the fighting to steal baradium munitions for a second attack on the Starhawk.
