Synopsis
Before the events of Dead Space, a planet mining colony funded by the Church of Unitology identified a Marker, an object sacred to the Unitologists' beliefs, on the planet Aegis VII. The Marker is a human copy of an alien object that has a fatal influence over the Aegis VII colony and the mining ship USG Ishimura, eventually causing an outbreak of reanimated mutated corpses referred to as "Necromorphs".
Aftermath is set in 2509, between the events of Dead Space, and Dead Space 2.
The USG O'Bannon was sent to investigate Aegis VII. After contact is lost with the ship, EarthGov sends another ship, which recovers four survivors; security officer Nicholas Kuttner, engineer Alejandro Borgas, chief science officer Nolan Stross, and chief medical officer Isabella Cho. En route to the EarthGov base at Titan Sprawl, each survivor gives their account, with EarthGov gathering intelligence for their own Marker project.
Kuttner led a team to stabilise Aegis VII's failing gravity. There they found fragments of the Marker, which were worth a lot of money. Touching a fragment caused Kuttner to have a psychotic episode and see visions of his deceased daughter. Before he could be restrained, he damaged the gravity stabiliser. After giving his account, Kuttner escapes and has another hallucination which leads him into space, where he dies.
Borgas's story reveals that the team failed to fix the stabilizer, and abandoned Aegis VII as it disintegrated, bringing back both the Marker shard and salvaged corpses from the Ishimura. Aegis VII's destruction damaged the drive and killed several crew members. While he is unaffected by the Marker, Borgas knows too much and is executed after the interrogation.
While studying its effects on corpses, Stross fell under the Marker's influence and unwittingly unleashed a Necromorph outbreak on the O'Bannon. When he went to protect his family, he suffered a hallucination that made him think they were Necromorphs, which caused him to kill them instead. Stross is kept alive so EarthGov can study the Marker's impact on his mind.
Cho's account reveals that she freed Kuttner to help fight off the Necromorphs, and partnering with Stross and Borgas they decided to throw the Marker shard into the ship's drive, hoping to both destroy it and jump-start the ship. By the time they reached the drive room, they were the only surviving crew members. Despite Stross' attempt to stop her, Cho threw the Marker shard into the ship's drive, causing a shockwave which disintegrated the Necromorphs but left the ship stranded. Now having arrived at the Sprawl, Cho deduces EarthGov's intentions of recreating the Marker.
When offered the chance to join the project, Cho refuses. She is lobotomised and framed as a terrorist responsible for the events on Aegis VII, the Ishimura, and the O'Bannon. Stross is held in an EarthGov asylum alongside series protagonist Isaac Clarke.