*CUT TO THE CHASE*
NOTE: This spoiler was submitted by Jeremy
The film opens in outer space where a capsule is floating amidst a meteor storm. The crew of the Pilgrim 7 attempt to get the capsule, as it contains a sample from Mars. Engineer Rory Adams (Ryan Reynolds) steps out and tries to catch the capsule with the ship's mechanism. The capsule slams into the mechanism, but it's been successfully caught.
Biologist Hugh Derry (Ariyon Bakare) studies the sample they recovered. It appears as an amoeba but slowly starts to grow its own limbs and even begins moving. The crew becomes elated when Hugh confirms that the specimen is alive.
On Earth, people around the world are following the crew's mission and the prospect of discovery of new life beyond Earth. Children from elementary schools around New York are gathered in Times Square as they send messages and questions live to the crew. One girl goes up to tell the crew that her school has decided to name the organism "Calvin".
Among the other crew members on the International Space Station are Dr. David Jordan (Jake Gyllenhaal), Captain Miranda North (Rebecca Ferguson), Commander Ekaterina "Kat" Golovkina (Olga Dihovichnaya), and pilot Sho Murakami (Hiroyuki Sanada). They all bond over their mission and personal lives, such as Sho's wife having their baby daughter back on Earth. As they continue to study Calvin, they learn that it possesses muscles, vision, and a brain.
A piece of equipment in the lab malfunctions, causing Calvin to go still and silent. After the equipment is fixed up, Hugh goes in and tries to revive Calvin with an electroshock wand. After a little jolt, Calvin wakes up and wraps himself around Hugh's right hand. He starts to grow in size and starts attaching himself to the glass plates. He grabs the wand and breaks it as he continues to tighten himself around Hugh's hand. Calvin then breaks Hugh's hand and causes him to pass out. Calvin grabs the broken wand and uses it to break through the glove in its containment cube. He then makes its way into a cage with the crew's lab rat. The rat makes a move on Calvin, so he wraps himself around the rat and consumes it, growing even more. Rory steps in to get Hugh out, but as he does so, Calvin wraps himself around Rory's leg, forcing David to close the door on Rory. Rory gets Calvin off his leg with an oxygen candle and tries to burn him with an incinerator, but he runs out of fuel. Calvin moves fast and crawls into Rory's mouth. He slowly kills him from the inside until Rory is no longer moving. Calvin crawls out and is even bigger as he escapes through a vent.
The crew wraps Rory's body in gold foil. Hugh states that the lack of oxygen on Mars is what probably kept something like Calvin dormant for so long, and he suggests that it could be responsible for wiping out life on Mars. The crew then tries to make contact with Earth, but their systems have been disrupted.
Kat puts on an EVA suit to step outside the station to fix the problem. Unfortunately, Calvin is outside and starts to wrap himself around Kat's suit. Kat starts to make her way back to the station, but Calvin cuts into her coolant system, causing her helmet to fill up with toxic fluids. David tries to get Kat back inside as she is drowning, but Kat intentionally leaves herself outside to prevent Calvin from getting back inside. Kat dies and her body floats out into space while Calvin tries to find a way back inside.
The remaining crew members are moving into a decaying orbit, and they need the rest of their fuel to get back into a proper orbit, even if it means letting Calvin back inside the station. The crew plans to deprive Calvin of oxygen by sealing themselves in their hibernation pods and venting the oxygen out of there. Hugh starts to go into cardiac arrest, so they bring the oxygen back, only to discover moments later that Calvin is latched onto Hugh's leg and is now bigger, with tentacles and something resembling a face. After he kills Hugh, the other three hide. Sho gets into his hibernation pod, which Calvin starts to break through.
Because Calvin swallowed a tracker from Hugh's suit, David and Miranda are able to keep their eyes on his movements. They try to lure Calvin away with Hugh's body. Soon, they find that Earth Control has sent a Soyuz capsule to get the crew back to Earth without bringing Calvin back. The station docks into the capsule, which gives Sho a chance to get out of his pod. As he tries to enter the capsule, a breach occurs from the imperfect docking, resulting in an explosion. This causes Sho to get sucked out of the station.
With the station's oxygen levels dropping and their trajectory headed back toward the decaying orbit, David and Miranda start to resign to their fates. They know that an attempt to make it back into Earth's atmosphere could kill them, but Calvin could survive it. David then remembers two escape pods on the station that they can use. One would get back to Earth while the other must be manually overridden to send Calvin into deep space. The plan is to once again deprive Calvin of oxygen to lure him into the pods.
David and Miranda go ahead with their plan. David lures Calvin into his pod while he tries to get Miranda home. The pods pass through a storm of debris, sending one pod off-course. Calvin attacks David inside his pod and begins to wrap himself around David.
One of the pods lands on Earth in the ocean near a boat with two fishermen. They make their way to the pod and discover David stuck in some kind of goo. Meanwhile, Miranda is sent helplessly screaming into deep space. David struggles to tell the fishermen not to open the pod, but they do so. Then, two more boats pull up.