In 2055, wars have ravaged the Earth due to the prevalent use of advanced military robots, and global warming and pollution have destroyed the environment and ruined the atmosphere. As a result, many people are born with birth defects and die, and large domes known as Skynets are built to protect the surviving cities on Earth. During the construction of the Skynet over B-16 (a futuristic Hong Kong), a meteor lands in the city and a giant alien plant, later named Pandora, emerges and causes devastation to the area around it as it takes root. Pandora grows rapidly when there is rain, taking over more of the city every time it does so; however, it is discovered that the plant can also purify the polluted air. ASU's (a local military force) lead scientist, Dr Chan (Tse Kwan-ho), finds a way to alter the plant's genome to stop Pandora from growing further while also letting it continue to repair the atmosphere. B-16 is going to get 2 rainstorms. The 1st rainstorm will only deliver 10 mm of rain, but the 2nd will deliver 160 mm of rain, allowing Pandora to grow and take over the entire B-16 and its 5.6 million population will be in danger.Tyler (Louis Koo) (principal force of B-16's Air Force who possesses extraordinary skills in operating fighter jets) and his friend Johnson Cheng (Sean Lau) (commander of B-16's Air Force and Tyler's brother-in-arms), soldiers working for the ASU, are tasked with locating Pandora's pistil and delivering a "gene bullet" virus that will neutralize its growth. Colonel Tam (Carina Lau) is sent to oversee the operation, but she has a backup plan to bomb Pandora from the air (before the 2nd rainstorm hits), which would destroy the plant but could potentially kill a hundred and sixty thousand people in the surrounding area. Cheng figures that Tam doesn't know a lot about how Pandora would react to the attack. They don't know how much time they will have to escape once the gene bullet is fired into the pistil. Cheng heavily opposes the idea of sacrificing civilians and losing their best chance to fix the atmosphere, and launches the mission before two rainstorms hit the city. Privates Connor (Wan Guopeng) and Lincoln join Tyler on the mission as they escort the Orca transport aircraft carrying the gene bullet virus into the operation area. During the mission, Sean Li (Nick Cheung), the commander in chief of B-16 and the architect of the Skynet project, sabotages the Orca by remotely taking control of its complement of military robots as soon as the first storm hits, and it crashes into a building. Damaged by Pandora's tendrils, Tyler's aircraft crashes after locating the area where the pistil is, and Lincoln is left critically injured.Connor and Tyler look for medical supplies at an abandoned hospital, where they are attacked by mantis-like creatures which kill Lincoln. Connor hides in the mortuary while Tyler retreats to an emergency room where he rescues an orphaned girl, Pansy, who reminds Tyler of his daughter Sissy, who had died of pollution-caused illness. Cheng, arriving in an armored car driven by former-squad mate Skunk/Yau Tai-long (Philip Keung) (a former member of B-16's Air Force who was dismissed after committing a major mistake and became at odds with Tyler. He was later recruited by Johnson to rejoin the force to participate in the plan to alter the genetics of "Pandora"), uses a hatchet to kill most of the mantis-like creatures while Tyler rescues Connor. The survivors escape the hospital and head to the building where the Orca crashed, finding the last intact gene bullet capsule and evidence that Li had sabotaged the mission in order to allow Pandora to be destroyed and the construction of his Skynets to continue. The team contact Li, saying that they have the evidence of his sabotage, but Li proposes a challenge: to beat him, they will have to go against the military robots under his control.As the team race towards the location of the pistil, Li sends several tank-like and humanoid robots after the armored car. As Skunk drives on, Tyler, Connor and Cheng fight off the robots, and Cheng becomes separated from the group after being thrown out of the car, in an attempt to fight off one of the larger robots. The others arrive at the location where the pistil is and encounter a large crab-like robot, with its pulse weapon destroying the armored car. Connor, Skunk and Tyler fight off more humanoid robots and destroy the crab-like robot, and Cheng returns and saves Pansy. Cheng enters the pistil chamber just as Pandora begins to grow uncontrollably as the second storm hits. Cheng unleashes the gene bullet virus onto Pandora, stopping it from growing further. Colonel Tam suspends the backup plan after discovering Li's sabotage, and Li commits suicide before she can arrest him. Afterwards, with the state of the atmosphere greatly improving, Tyler accepts a mission on the moon while Skunk and Cheng finish rebuilding the armored car.