After a NASA space probe searching for extraterrestrial life crash-lands in Mexico, creatures begin to appear at the US/Mexico border and the area is quarantined. Troops fight to contain the creatures and a border wall is built to keep them out of the US. American photojournalist Andrew Kaulder (Scott McNairy) receives a phone call from his employer, telling him to find his daughter Samantha Wyden (Whitney Able) and take her back to the US.

Andrew finds her in a Mexican hospital, and they try to return by train, but the tracks are damaged. If they cannot get out in a few days, sea and air travel will be impossible for six months. They decide to hitchhike to the coast. Andrew buys Samantha a ferry ticket, but he ends up sleeping with a woman who steals their passports. Samantha has to trade her engagement ring for passage through the quarantine zone.

They travel by riverboat, then are led by armed escorts overland to the border. Creatures attack the convoy, and the guards are killed, but Andrew and Samantha escape. They find the bodies of travellers and bond atop an ancient pyramid in sight of the border. The creatures have crossed into the US. They pass through an evacuated town in Texas and call for help from an abandoned gas station. Beautiful alien creatures arrive, communicate with each other and perhaps mate. Sam and Andrew kiss and are rescued by the US army.

This was a low-budget science-fiction film written and directed by Gareth Edwards, his first. He was also cinematographer, production designer, and visual effects designer. It was made by six people in five countries, often without permission. The entire team travelled in one van with their equipment. The extras were locals persuaded to appear and their dialogue was improvised. It received good reviews and was a box-office success. It was, in fact, small and relaxed and at times quite beautiful. It cost less than half a million dollars. It was nominated for six British Independent Film Awards and won three of them. The two lead actors are now married and have two children.