Journey partner to Life Partner...

After the cancellation of their flights out of Boise Airport due to stormy weather, neurosurgeon Dr. Ben Bass (Idris Elba) and photojournalist Alex Martin (Kate Winslet) contact Walter (Beau Bridges), a local private pilot to get to Alex's wedding (scheduled for the following day) and Ben's emergency surgery appointment in Baltimore, Maryland. They board an uncharted flight with Walter's dog. Shortly after takeoff, Walter suffers a stroke, causing the plane to crash on a mountaintop. Ben, Alex and the dog survive the incident with various injuries, but Walter is killed.

Ben buries Walter and tends to Alex's wounds, realizing they must find civilization for any hope of survival. Alex asks Ben to leave her behind as he has a better chance of surviving, but Ben refuses. Instead, he climbs a peak to see if there are any structures nearby. On his descent, he nearly falls off a cliff face. Meanwhile, a cougar approaches the plane wreckage, attacking and injuring the dog. The cougar then approaches Alex within the plane wreckage, but she wounds it with a flare. Ben returns to find a blood trail and rushes to the plane. He provides medical attention to the dog and later retrieves the body of the cougar and barbecues it for food.

Stranded for days with dwindling sustenance, Ben and Alex find strength in each other. Alex becomes skeptical that help will come, though Ben continues to insist they wait for help. After a heated argument, they both sleep, with Alex resolving that she will leave. At first light, she proceeds to leave the wreckage and start a descent down the mountain. Ben wakes and gives chase, eventually catching up with Alex, and they make up over past grievances. While making shelter in a cave, Alex uses her camera to locate a man-made structure and spots a reflective material flashing at her. They agree to make it down to this structure. As they continue their walk, they become separated from the dog. Ben goes after him and finds an abandoned cabin. As he looks through it, Alex feels the ground beneath her cracking. She realizes she is standing over thin ice, and she falls through into the ice cold water. Ben hears the cracking and sees Alex fall down. He runs over and pulls her out, but she is unconscious and almost blue. Ben brings her to the cabin and starts a fire to warm her up. He takes a risk of administrating her an injection he crafted out of materials in the cabin in a resourceful way. A couple of days later, Alex eventually wakes up to the sound Ben makes with the piano in the cabin.

The first time Ben leaves Alex alone in the cabin, she goes through his personal things and again listens to a voicemail recording from his wife. Ben catches Alex in the act. She says she didn't mean to be nosy, but she just wants to know something about him, especially since he has disclosed so little about himself and he never talks about his wife. He finally tells her his wife died two years ago from a brain tumour.

When Ben tells Alex he is going outside to get more wood for the fire, the culmination of all of their experiences together finally overcomes them. No longer able to resist each other, they have sex. As Ben sleeps afterwards, Alex takes his picture. Deciding that they still won't make it, Alex again asks Ben to leave her behind to find help and return. Ben initially agrees but has regrets about leaving her behind just for a moment. He returns once more and they begin to press forward again. As they make their way down, Alex begins to tire quickly. However, Ben still refuses to leave her behind. They fall asleep in the woods. Eventually, they find a timber yard on the mountain and they make their way to it. Ben gets his leg caught in a bear trap. Alex keeps going and she's rescued by a truck driver, who goes back and rescues Ben.

Ben wakes up in the hospital and goes to Alex's room, where he sees her with Mark, her fiancé. Mark praises Ben for saving Alex, to which Ben replies she saved him, and leaves the room, heartbroken. Some time after, Mark tells Alex that "I told myself that if you ever lost a part of you (an arm or leg in her dangerous job as a photojournalist), I would still love you." But now, it's obvious to him that he has lost her heart.

Alex tries calling Ben, but he declines her phone calls until he receives pictures of him and Alex on the mountain. This encourages Ben to call Alex. They meet up at a restaurant in Manhattan, where it is revealed that Alex is now a part-time teacher who is uncomfortable flying, and Ben is now working as a consultant in trauma clinics as his frostbitten hands have not recovered enough for him to operate. Ben admits that he did not call her back because he thought she would be married, and Alex responds by saying that she couldn't go through with it and she loved Ben while they were together on the mountain. After leaving the restaurant, Ben admits to Alex that they survived because they fell in love. She dismisses her feelings and reminds him of what he said before on the mountain- that 'the heart is just a muscle.' They hug goodbye and as they depart in opposite directions, they feel deep regrets, burst into tears and run back into each other's arms.