The Battle for Horizon Base unfolded during the war that pitted the First Order against the Resistance. In this conflict, Poe Dameron, Finn, and Gannis Ducain embarked on a mission to the Horizon Base outpost. Their objective was to enlist the aid of the Oruan resistance group who had sought refuge there following the First Order's conquest of their homeworld, Oru. Despite initial reluctance from Mezlo, the Oruan leader, he ultimately pledged to offer assistance if the Resistance ever called upon them. After a series of brief skirmishes with First Order stormtroopers within the station, the Resistance team made their escape aboard the Millennium Falcon.
Finn, while evading stormtroopers at Horizon Base, contacted Poe Dameron to report that the mission was off track. Poe emphasized the mission's critical importance to the Resistance and that General Leia was depending on him. He then inquired if Finn's partner was capable of handling the situation. Gannis Ducain appeared behind Finn, assuring him that he had learned from his past mistake of stealing the Millennium Falcon.
As Finn and Ducain conversed, a stormtrooper approached, demanding identification. Instead, Finn triggered the release of barrels suspended above the stormtroopers, causing them to fall. Finn and Ducain then fled into the base, where Ducain confessed his past errors and expressed doubts about his suitability for the mission. Finn reassured him that he was now a member of the Resistance and that his past was behind him. However, their conversation was interrupted by a Candori that seized both Finn and Gannis.
Below them stood Mezlo, the leader of the Oru resistance, who was using the Candori as a shield against what he believed were First Order personnel. Finn and Gannis identified themselves to Mezlo as members of the Resistance, offering their assistance. Mezlo instructed the Candori to release them but declined to join the Resistance. He recounted how he nearly defeated the First Order on his planet, despite their forces outnumbering his resistance tenfold. He voiced his belief that the Resistance lacked the strength and fighting spirit needed to confront the First Order. Finn and Ducain shared their stories of joining the Resistance, prompting Mezlo to briefly reconsider, impressed by their dedication. However, they were discovered by stormtroopers who ordered them to freeze. But another Candori emerged from behind the stormtroopers and captured them. Finn contacted Poe, requesting a pickup at Hangar Five in the Falcon as a firefight erupted. Finn renewed his plea for Mezlo to join the Resistance, but he remained steadfast in his refusal. As they made their escape, Mezlo promised to answer the Resistance's call for aid when the time came.
Aboard the Millennium Falcon, Finn informed Poe that the Oru resistance would not be joining their cause. Poe expressed concern, noting that they were still on their own. However, Finn countered that while the First Order possessed superior manpower and firepower, Ducain pointed out they lacked honor. He also asserted that the Oruans would fight alongside them when the moment was right, and they would not be alone.