Ash 2025

An astronaut, Riya, abruptly wakes up aboard a scientific research station on a distant, barren planet, with no recollection of where she is, how she got there or what happened to her, apart from some nightmarish memory fragments. As she explores the station, she finds several corpses and then hears someone entering through the station’s airlock. Ambushing the arrival, Riya discovers that it is a man naming himself Brion, who claims to know her and to have come here after receiving a distress call from her.

In the course of Riya and Brion’s investigation, supplemented by occasional flashbacks, it is revealed that Riya, Brion and the deceased crew - Adhi (the crew’s command officer), Kevin (Riya’s boyfriend), Clarke and Davis - were part of several exploratory expeditions from Earth to discover new habitable planets. With the other six expeditions lost, the latest discovery - the planet they’re on, designated K.O.I.-442 and nicknamed “Ash” by Kevin - is Earth’s last hope for success. While the others inhabited the planetside station, Brion stayed on a second station in orbit to maintain contact with Earth and monitor the crew’s progress.

After unsuccessfully trying to find a trace of Clarke (the only crew member not found among the dead), Riya and Brion make preparations to leave the planet within twelve hours and reach the orbital facility, as the ground station’s systems are compromised and life support is failing. Riya begins to experience more frequent flashbacks of her crew dying horrifically, including by her own hands. During a meteor storm, the station’s systems register a hull breach. While working to seal the breach, Riya finds signs of someone having been inside the maintenance shafts, and based on her flashbacks, she suspects that Clarke is still alive and was infected by something unknown which caused her to become psychotic, thus making her responsible for the crew’s death and now the station’s sabotage.

With the station’s oxygen supply even more depleted, Riya and Brion must leave on the very first line-up with the orbital station or else suffocate. In a drone’s memory bank, Riya finds recordings of an EVA investigation after Brion discovered strange emissions from multiple points on the planet, yielding the discovery of atmospheric converters of alien origin. When Davis descended into a converter’s shaft, he was killed when the devices suddenly activated and a rock fragment was propelled right into his face at high speed. She berates Brion for not telling her before, and she also remembers that she killed Kevin and Adhi, although she cannot remember the reason. Brion refuses to stay, insisting that the revelation of advanced alien life and functional terraforming comes before finding out what happened.

With two and a half hours left before Brion’s lander intitiates automatic takeoff, he and Riya prepare for evacuation when Riya has a sudden flashback of Adhi aggressively attacking her, forcing her to kill him in self-defense. After recovering, she finds an intruder in an EVA suit - Clarke - aboard the station, and flees into the maintenance tunnels, where she finds Brion dead. With Clarke attacking her, Riya retreats to the station’s bathroom, where she plugs a shower hose into Clarke’s helmet and turns the water on, drowning her. But upon scanning Clarke’s body, Riya finds no trace of infection in her, and with the orbital line-up imminent, she is forced to leave for the lander, only to find it sabotaged. Returning to the station, she scans Brion’s body and is startled to discover that he had died long before she encountered him.

Upon this discovery, Riya realizes to her shock that she is the one infected and that Brion’s presence on the station was just a hallucination caused by a nanotechnological parasite residing in her. An alien invertebrate had been inadvertently brought to the ground station by Kevin and infested its mainframe and airlock, disrupting contact with orbital and forcing Brion to come down. Ahdi and the others had argued for immediate evacuation, but Riya insisted on staying to investigate and recover the terraforming technology. While researching the alien, she found it infected by the parasite, which broke out and infected Ahdi, making him attack the rest of the crew. When Kevin killed Adhi, the parasite abandoned him and infected Kevin, who chased the fleeing Brion into the maintenance shafts and killed him there. After sending Clarke to the safety of the lander, Riya stayed behind to confront the alien and killed Kevin, whereupon the parasite infected her. Seeking to kill herself before it could fully take hold of her, Riya ingested potassium cyanide from the station’s sick bay, but survived when the parasite neutralized the toxin. When Clarke returned later, Riya killed her by mistake because they both believed each other possessed.

The parasite informs Riya that its race has claimed this planet before the humans found it, and that, since it found the human race an inefficient life form, it has chosen to merge with and evolve her. Refusing to submit, she has the parasite extracted by the station’s medbot, but it infests and revives Brion’s corpse and attacks her. Riya kills it with a welding torch, and after exiting the burning station, she restores the lander to full operation and takes off towards the orbital facility, which, however, is already infested by more parasites.