In the near future, a Chinese spaceship comes back to Earth with a newly discovered energy
source called "xianteng". Within just a few years, it replaces traditional energy sources,
and cities see unprecedented and super fast development. Unfortunately using so much of
this energy also gets the attention of a species of aliens that one day bring their ships to attack
all the major cities across the globe as revenge for stealing the xianteng. The attack comes as a
total surprise and leaves all the cities in ruins without xianteng to depend on. Eventually the
leaders of 97 countries hold an emergency meeting in Shanghai to create a unique defense system to
save the last standing city in the world. Using a simulation that plays the aliens sending their
flying robots for another attack, the Grey Eagle Team, formed by Jiang, Zeng Yu, Yiyi, and Pan,
controls the latest models of military drones to engage the robots in battle. Their teamwork
is excellent because they each have skills that complement each other and they were trained by
Commander Lin Lan herself. Commander Yiyun is very happy with the results and notices Jiang
is particularly good at piloting, Lin Lan confirms this by saying he's the best by far. It turns out
Jiang used to be part of the logistic team that built the Shanghai cannon, which has allowed
Shanghai to be the last standing fortress. But as things got worst he joined the battling team to
help. After another day spent training, Jiang leaves the office and rushes to the elevator
so he can leave with Lin Lan, who Jiang has a huge crush on. Today it's Lin Lan's birthday,
and Jiang wants to gift her a flower, but he's shy and hesitant. By the time he gathers courage,
Lin Lan is already leaving the elevator. Later at home, Jiang sends her a message about today's
training and is delighted to see her answer he did well. Sometime later, Yiyun informs Lin Lan that
New Delhi has also fallen to an alien attack and he wants her to use the information gathered there
to improve their defenses. Suddenly code red is announced in the fortress: it turns out an alien
mothership has appeared above Shanghai. People begin panicking all over the city, but soon the
soldiers guide them to the corresponding shelters before joining their teams at the fortress. Among
their many defenses, the city has a special force field that stops the laser beam the mothership
opens its attack with. However the force field can't stand up for long, and when the beam manages
to make a hole, the aliens send an army of robots through it before the engineers fix it. The pilots
immediately send their drones to fight them, being careful not to hurt any civilian that is still
running to a shelter. One of the robots approaches the fortress and lands in the middle of the road,
causing a car accident that almost hits a girl - luckily Jiang pushes her out of the way just in
time. Then the robot begins shooting at everything in its path, so the artillery team opens fire to
try to stop it, to no avail. Jiang tries to help as well without much luck, but at that moment a
tank controlled by Lin Lan arrives and destroys it in seconds. The drones finish taking down the rest
of the robots just in time for the engineers to finish fixing the force field, thus the mothership
leaves the area for now. Later, the science division inform the committee that they scanned
the mothership during the fight and discovered a weak point in it. The committee wants to use the
Shanghai cannon to hit it, but Yiyun doesn't let them because a counter-attack could put people's
lives at risk. Afterward Yiyun takes Lin Lan to a secure facility to explain that Shanghai has the
last deposit of xianteng, which is highly unstable and the only thing that keeps the city going,
including the fortress and the force field. If they shoot the cannon, they would waste all the
remaining xianteng and leave the city defenseless. The best way to keep the aliens at bay is to
continue training their Eagle team so they can replace the force field one day. Meanwhile Jiang
and his friends are hanging out on a rooftop, sharing a drink and their dreams about what they'd
do with their lives if they weren’t at war. Pan in particular wants to finish his bike and ride
it freely. They're suddenly interrupted by an emergency call that announces the city is under
attack again, so they rush back to the fortress, ready to fight. As usual the force field comes up
to stop the incoming beams, however Pan notices something weird. While many holes in the shield
have been achieved, the enemy robots still don't attack. This makes him realize this is a trap,
the aliens are making them repair the field over and over so they'll run out of xianteng and the
city will be defenseless. The next time a beam goes through the field, it causes lots of damage
inside the fortress, and the robots finally make their way in. The soldiers have no choice but to
fight face-to-face, but mere bullets aren't enough, and many of them die in the process.
The Eagles join the battle as backup to help, but they can't do much and prefer to go inside
to gain control of the drones. While the Eagles use the drones to begin fixing the force field,
the committee goes against Yiyun's orders and sends a man to activate the cannon. They don't
use the full power to avoid losing all their xianteng, but it hits the mothership hard enough.
The Eagles also successfully finish repairing the field, so the mothership has no choice but
to go away. Nearby, a robot reveals not to be as destroyed as they thought. Later in the evening,
the Eagles spend some time with their personal hobbies, and Jiang dares to finally invite Lin
Lan on a bike ride. However this turns out to be a dream, but when Jiang wakes up he discovers
there is other good news: the Eagles have been promoted thanks to their amazing performance last
night. Yiyi decides they need to celebrate their promotion, and the team goes to a club to have
fun, but Jiang can't stop thinking about Lin Lan. While he's brooding on the roof, Yiyi notices his
mood and advises him not to be afraid to confess his feelings to Lin Lan because who knows if the
aliens will let him do so in the future. Sometime later, the team watches on tv how the man that
shot the cannon gets an even better promotion, and during his speech, he makes reference to a loved
one. Jiang thinks this is Lin Lan and gets in a very blue mood. Later in the evening, Jiang goes
to a noodle restaurant for dinner and is surprised to find Lin Lan there. They discuss the pressure
of having to save the world and lament the lives lost in battle. Seeing how tense Lin Lan is,
Jiang is finally brave enough to give her the gift as a way to cheer her up. After she leaves, Jiang
sends her a message asking her to meet the next day, and he's delighted to see she accepts. The
next day, Pan and Zeng Yu put Jiang in a leather jacket to impress his date. However Yiyi thinks
it's not fitting and makes him wear his uniform instead. Moments later, Jiang meets with Lin
Lan and is disappointed to hear she only wanted to meet to check on the generators. While Jiang
does the maintenance, Lin Lan tells him about her training days and how her father had been a cold
soldier that died in battle. Lin Lan can't help crying at the memory, and as she watches the sky,
she tells Jiang that she hopes they can build a future where kids can look up and see the stars
instead of the beams that keep up the force field. Sometime later, people panic when they notice that
the ground is starting to split, almost as if an invisible earthquake has hit the area. Yiyun
tells the committee that the energy deposits aren't stable and the use of the cannon has
made it worse, meaning there's a risk of the force field will go down soon. Suddenly an alert warns
them that cracks have mysteriously appeared on the force field, so Yiyun rushes back to the command
center to guide the Eagles into repairing them. Thanks to skillful teamwork, the field goes back
to normal, but at this rate it is only temporary. At that moment, a robot breaks through the roof
into the command center and begins killing people. The soldiers try to stop it with their guns, but
bullets can't damage it. Pan tries hitting it with a fire extinguisher but it doesn't do anything
either, and the robot doesn't hesitate to hit Pan in return before dragging him to the force field
panel to disable it. With his dying breath, Pan activates the self-destruct sequence, and Jiang
and Zeng Yu have to drag a crying Yiyi out before the room explodes. With the robot destroyed,
the force field goes back up immediately. In the evening, the team takes a moment to mourn
Pan and the other casualties with the respect they deserve, and Yiyi's given Pan's tags. When
they return to their dorms, Jiang gives Yiyi Pan's bike key because he had always wanted her to have
it. Sometime later, the committee discusses the option of giving up on Shanghai, but Yiyun refuses
and reveals he's made a battle plan for their last chance. The idea is to shut down the force field
and direct all that power to the cannon so that it'll be strong enough to actually destroy the
mothership. The Eagles will have to be the defense instead of the shield, and the team accepts the
mission even if it's incredibly dangerous. Yiyun also asks Lin Lan to stay in the xianteng room
and stand on guard. All civilians are sent away to shelters until the streets are completely empty,
this will allow soldiers to fight more freely and have tanks on every corner. Before they join the
fight, each soldier leaves an item inside a box that will last one hundred years in case the city
falls to ruins too. Zeng Yu leaves a letter for his parents, and Yiyi leaves Pan's keys. Jiang
chooses his phone, but first he sends a message to Lin Lang confessing his feelings. Unfortunately
because of the current power problems, it isn't sent. This time the Eagles will have to fly actual
planes instead of controlling the drones. As soon as the force field is shut down, the alien robots
descend and start a fierce fight in the sky. The Eagles coordinate their skills in the air together
with an army of drones, but unfortunately it isn't enough and a few robots fly past them to attack
the command center. With encouraging last words for his team, Yiyun dies when the room explodes.
Next the robots begin making their way to the xianteng facility, so the Eagles and the tanks
rush to try to stop them. As another battle begins with both sides losing soldiers every second, Lin
Lan checks on the cannon and discovers it's fully charged, they only need to wait for the mothership
to get in the right position. The robots manage to break the line of defense on the ground, and one
of them jumps on Yiyi's plane. Jiang asks her to do a flip and flies closer to hit the robot with
his own plane, effectively destroying the enemy but also catching his own wing on fire. Jiang has
no choice but to evacuate in the emergency pod, which lands right in the middle of the battle.
He immediately joins the fight with his guns, shooting at the robots as close as possible,
and when a robot is about to kill him, Yiyi shows up and shoots it with her plane. Then she joins
the fight on foot as well, determined to get revenge for Pan. Meanwhile Zeng Yu flies toward
the mothership to try to make it move toward the cannon. There are too many robots surrounding him
though, so he needs backup. Yiyi rushes back to the command center and while thinking about Pan,
she activates a special grenade that takes out a good amount of robots, sacrificing herself in
the process. While Jiang rejoins Zeng Yu in the air by using Yiyi's plane, the mothership finally
moves. The cannon is immediately shot, causing a huge explosion that also damages the surrounding
buildings. When the air clears, everyone is shocked to discover the attack has failed because
the robots took the shot to defend the mothership. With almost no hope left, Lin Lan remembers why
Yiyun left her there: the cannon was shot with the energy from the force field, but as a last resort,
they can shoot one more time with the remaining xianteng energy. This will leave the city
powerless and cause the land to sink. Accepting the risks, the cannon begins recharging while
Zeng Yu and Jiang continue to protect it. A robot manages to sneak inside the xianteng facility and
begins killing every person in its way, but at that moment, Lin Lan pulls the lever and activates
the last resort. All the buildings and the land begin sinking, bringing down the robot with them,
and Lin Lan offers a heartfelt speech before dying that makes Jiang cry. To make matters worse,
the soldiers discover that the cannon's guidance system was damaged during the sinking. Jiang tells
them to open the infrared guidance device and lock it in his position so he can guide the cannon,
and Zeng Yu flies ahead to clean the way. The robots take the bait and go after him, and Zeng
Yu self-destructs to bring them down with him. Now that the mothership has no protection, Jiang flies
right into it to serve as a guide and the cannon shoots its last charge, finally destroying the
ship for good. As days pass, Shanghai is slowly rebuilt with the effort of traditional technology
instead of xianteng. It's then revealed that Jian has survived by ejecting the pod right before the
cannon hit, and now he's been given the highest promotion. However he still misses his team
terribly and likes to revisit the places where they used to hang out. One evening he visits the
noodle restaurant, and a coworker brings him the box where he left his phone. When Jiang checks it,
he's discovered that his confession had been sent and Lin Lan only replied "received". With tears
in his eyes, Jiang sends her one last message, telling her to "sleep well". Then a flashback
reveals that when Jiang chose to join the army, he had Lin Lan's guidance on how to fill in the form.
He fell in love with her that day and that's why he chose the fortress as his destination.