Ash

Riya wakes up aboard a scientific research station on a distant, barren planet with no recollection of how she got there. While exploring the station, she suffers nightmarish flashbacks and finds several corpses. She encounters a man named Brion, who claims to be a companion responding to her distress call. An investigation reveals that Riya, Brion, and the deceased crew—command officer Adhi, Riya's boyfriend Kevin, Clarke, and Davis—were part of several expeditions to discover new habitable planets. The planet they are currently on, designated K.O.I-442 (nicknamed "Ash"), is Earth's last hope for success. While the crew inhabited the planetside station, Brion stayed on a second station in orbit to maintain contact with Earth and monitor the crew's progress.
Riya and Brion fail to find Clarke, the only crew member whose corpse was not among the dead, and make preparations to leave the planet. Riya begins to experience more flashbacks of murdering the crew. 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. She suspects that Clarke is still alive and was infected by something unknown, which caused her to become psychotic and made her responsible for the crew's death and the station's sabotage.
Due to the station's oxygen supply rapidly depleting, Riya and Brion must leave on the first line-up with the orbital station. 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. Brion tells her that when Davis dropped a rock into the converter's shaft, the device suddenly activated, propelling the rock back up and killing him. Riya and Brion have an argument where he refuses to stay, insisting that the revelation of advanced alien life comes before finding out what happened.
Brion and Riya prepare for evacuation when she suddenly has a flashback of Adhi aggressively attacking her, forcing her to kill him. After recovering, she encounters Clarke, who flees into the maintenance tunnels. Riya follows and finds Brion's corpse. Clarke attacks her, and Riya retreats into the station's bathroom, where she plugs a shower hose into Clarke's helmet and drowns her. Upon scanning Clarke's body, Riya finds no trace of infection. She is forced to return to the lander but finds it sabotaged. She returns to the station and scans Brion's body, discovering that he had died before she met him.
Riya realizes that she is the one infected, and she hallucinated Brion due to a nanotechnological parasite residing in her. It is revealed that Kevin inadvertently brought an alien invertebrate that disrupted contact with orbital and forced Brion to come down. Adhi and the others argued for immediate evacuation, but Riya insisted on staying to investigate and recover the terraforming technology. While researching the alien, a parasite broke out and infected Adhi, causing him to attack the crew. After killing Adhi, Kevin became infected and kills Brion. Then, Riya killed Kevin, and 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.
The parasite informs Riya that its race has already claimed this planet. Believing the human race to be an inefficient life form, it has chosen to merge with and evolve her. Riya extracts the parasite, but it infests and revives Brion. She kills it with a welding torch and restores the lander, taking off toward the orbital facility. As she nears it, it's revealed that the facility has been overtaken by a large parasitic entity.