A star system in the Local Cluster.
A primitive alien species exists here, and an asari expedition was observing them when they were ambushed by a group of human colonists who took one of the asari prisoner. Hoping to avoid inflaming the situation, the Asari Republics turned to the Systems Alliance for aid in maintaining peace. At first, this proved quite difficult as the Alliance had no record of any colony at Alpha Centauri, despite its status as a neighbouring system to Sol.
Further reconnaissance and record checking by the Alliance revealed that the colonists were members of the Manswell Expedition of 2070. The Manswell Expedition was a private spaceflight venture funded by Victor Manswell, a billionaire frustrated by the pace of official space exploration. Around 300 people were placed in cryogenic freeze for Manswell's expedition, departing Earth in 2075, roughly 75 years before humanity's discovery of the Mass Relays and contact with the other races of the galaxy. After launch, contact was lost with the expedition.
Believing it very possible that the colonists had no knowledge of the rest of the galaxy, the Alliance decided to proceed using first contact protocols. Rather than send in a full military force, they sent in a team of military experts, medics, sociologists, anthropologists, linguists, psychologists, geneticists, and other experts to a facilitate a dialogue with the colonists. Unfortunately, the colonists viewed the gesture as part of an alien plot and put up a spirited defense. Several were wounded on both sides before the violence was quelled. After finally convincing the colonists that they were actually humans from Earth, an Alliance representative was allowed into the colonists' camp to speak with the colonial leader and check on the condition of the captured asari scientist.
Resolution and Aftermath
Following the release of the asari scientist, who was in good condition, the Alliance offered to help assimilate the colonists back into human society and the galactic community. Attitudes on how to proceed were roughly split evenly within the colony. Some colonists felt that the changes in the past 120 years would be too much to adjust to and opted to stay on the colony. Others were eager to return the galactic community, with one expressing amazement that they had descendants still alive.