When a relief ship arrives at an outpost on Jupiter’s moon Callisto, the ship’s inexperienced commander must investigate the disappearance of most of the previous crew in the face of escalating paranoia and the remaining scientist’s claim of an alien presence.

SYNOPSIS:

ELIZABETH HELMFORD never intended to be alone 600 million miles from home. But when Mark Ailesworth, her companion on the scientific outpost on Jupiter’s moon Callisto, dies unexpectedly, she is suddenly more alone than any human being has ever been; even radio communication back to Mission Control takes two hours round trip. With the relief crew not scheduled to arrive for more than two months, isolation quickly takes its toll on Elizabeth.

So when she hears someone knocking on the station’s door, she’s as much worried about her sanity as her safety. Of course, there can’t be anyone there, but “Open the door,” Control instructs her, and Elizabeth almost complies. Almost, that is, until she realizes that the conversation she’s having with Control is happening, impossibly, in real time, and that maybe what is claiming to be Control is something else. As her anxiety mounts, Elizabeth struggles to separate delusion from reality, fighting to retain control right up to the moment that the voice comes from behind her, and a shadow falls on her…

71 days later, right on schedule, the relief ship Garuda arrives. When Mission Commander AMAYA CHAKRABARTI, pilot DANIEL MCKENZIE, and Mission Specialist KENZO OTREYU enter the station, the lights are on, but nobody’s home – there’s no sign of Elizabeth. And when Kenzo searches the logs, he finds unsent transmissions to Mission Control, the conversations that Elizabeth thought she was having with home, but hers is the only voice is on the recordings.

With nothing else to go on, the crew gets started on their own mission. But even as they do, history seems to be repeating itself as someone, or something, knocks on the door. Against Daniel’s objections, Amaya orders them to open the airlock door – with no camera outside, they have no other way of determining who or what is out there. What’s waiting for them is the last thing they expected: Elizabeth.

Dazed, dehydrated, confused, Elizabeth seems to be unable to answer where she’s been all this time, and Daniel’s belligerent questioning only adds to her distress. As a woman in a command position, Amaya understands the need to assert control: she shuts Daniel down, sends him to quarters, using the opportunity to bond with Elizabeth, who opens up to her, confiding that she not just heard but saw something. Disturbed by the implications, Amaya secretly records the conversation, and relays the information to Kenzo and Daniel as the trio agree to send the recording back to Control for instructions.

Daniel’s mounting paranoia may be being proven right as the crew attempts to proceed with their mission; Elizabeth eagerly volunteers to help, wanting to make herself useful, but she seems unsure of some of her responsibilities, and the station’s security system fails to recognize her retinal scan at first.

And when he finds her sitting at her workstation, she insists that the camera is watching her. In his efforts to contradict her, Daniel accidentally triggers the recording that Amaya made and sent. Elizabeth erupts into a violent meltdown, insisting that they’re playing into “its” hands. As the trio attempts to subdue her, an alarm goes off indicating that someone is trying to open the main airlock; on the monitor, they’re stunned to see a spacesuited figure, and even more stunned when it turns and looks into the camera, clearly showing its face inside the helmet: Elizabeth’s face.

Chaos erupts. Elizabeth is locked away but in the struggle the figure at the airlock disappears. Amaya and Kenzo follow it out onto the moon’s surface, with the increasingly mutinous Daniel left to guard the prisoner. Elizabeth begs to be released, swearing she is who she claims to be, even sharing memories of her time with Daniel in training; Daniel wavers, but insists he’ll wait until Control radios instructions.

Amaya and Kenzo follow tracks on the surface until they suddenly just end. Spooked, they make their way back to the Station, passing the bodybag containing Ailesworth. Desperate for clues to what is going on, Kenzo impulsively opens it: inside they are shocked to find the frozen corpse of Elizabeth!

Hauling the body inside, they confront ‘Elizabeth,’ and she breaks down, confessing that she was confronted by an alien lifeform, but that rather than threatening her, it was seeking to save her; it had come to study humanity, but instead had been trapped on this moon after being infected with a virus that could mimic other life forms. It couldn’t return to its home world for fear for taking the virus with it. Kenzo assures them that that makes no sense, there’s no ecosystem for a virus on the moon, but Amaya points to the evidence in front of their eye: to prove it, Elizabeth offers to lead them to its ship.

Amaya can’t pass up the possibility that Elizabeth is telling the truth. Daniel refuses to accompany them, informing Control of his intention to relieve Amaya of command, but Control’s response references Ailesworth’s body being brought inside, which the crew had not reported yet. Convinced now that there is something there with him, Daniel searches the station, but is ambushed and knocked unconscious.

On the surface, there’s no ship to be found, and Elizabeth has vanished. Daniel, coming to, realizes with horror the figure that attacked him was Kenzo! He suits up and escapes to the surface through a secondary airlock, trying to warn Amaya even as Amaya and Kenzo reach the station…but find themselves locked out by Elizabeth. No longer sure of anyone’s identity, including her own, she sets in motion the destruction of the station, arguing that none of them should make it home.

As Amaya pleads with Elizabeth, Daniel finally arrives. He immediately attacks Kenzo, slashing his air hose, and Amaya in turn attacks him, smashing his face plate. Alone now, she begs Elizabeth to let her in. How do I know you’re you, Elizabeth asks, or I’m me? Amaya points out that Elizabeth remembered Daniel, but what if the virus is so sophisticated that it can mimic not just flesh and bone, but mind, memory…At that point, Amaya says, what does it matter? Elizabeth concedes; the door opens.

The two women board the Garuda for the long flight home. Elizabeth listens in dawning horror as Amaya radios back to Control that she is returning home: she, Elizabeth Henstridge, sole survivor of the Callisto mission, because the voice she is hearing is not Amaya’s but her own. She turns to Amaya, to see her own face staring back at her from the other seat. It smiles. The Garuda lifts off, heading for Earth.