In South Korea, the underground oil pipeline system is about 1200km long. Crude oil is
refined at various refineries and transported to major cities via pipeline every week.
There are people who drill into it to siphon oil and make money, they're known as "moles".
Criminal Straw is interested in this business, so he hires the legendary Drill-Bit to get the job
done. However, the one that shows up is Jeob-Sae pretending to be Drill-Bit, so when he tries to
work with the same drill the famous mole uses, he screws up and causes a leak. The warehouse ends up
exploding, and the men manage to escape alive just in time, but Jeob-Sae gets his legs burnt. A few
hours later, the police arrive to investigate the crime scene, and as soon as police officer Man-Sik
sees the drill that caused the explosion, he is sure this is the work of Drill-Bit, who he caught
in the past when he used to work in the intel division. He doesn't tell the higher-ups about
this though, because he's lost all credibility, so Man-Sik asks his partner Sang-Goo to help him do
the investigation on their own. Meanwhile, Straw goes to see Dae-Han, the mole that sent him the
fake driller because the real Drill-Bit is too expensive. Straw beats up Dae-Han and demands to
see the real genius, so later, Dae-Han arranges a meeting with Dol-Yi, the actual Drill-Bit.
While they discuss the details, Man-Sik and Sang-Goo arrive to accuse them of being behind the
recent explosion and ask them to show their legs, but the lack of scarring puts them in the clear.
Afterward, Man-Sik tries to convince his boss that the moles will try again, but he's ignored,
so instead, Man-Sik convinces Sang-Goo to help him check out all the abandoned buildings in the area.
Back to Dol-Yi, he meets with Straw to finish the job Jeob-Sae failed to do, and Straw is so
pleased by the success that tells Dol-Yi about an incoming bigger job from an important backer.
A few hours later, Dol-Yi has a meeting with this backer, who turns out to be Geon-Woo,
a rich oil refining company owner. Geon-Woo wants him to drill too particular dangerous
holes and get enough oil to fill the tanks of a factory that will be bulldozed in fifty days,
so the job should be done in a month. Dol-Yi thinks rushing the job will make it go badly,
but Geon-Woo convinces him to join by accepting to pay him one million. The job is happening in the
basement of a hotel that will be closed with the excuse they're full. Dol-Yi will be the leader of
a team carefully chosen for the task: underground geography mapper Mr. Na, excavator Geun-Sab,
and welder Jeob-Sae. While the men work, Counter will watch over the reception desk to keep any
bystanders away. If the cops ever come by, she'll activate an alarm to warn the team.
While they're getting half of the pay in advance, there's a catch: if any of them leave the hotel
before the job is done, the contract is void. All their phones are taken away by Straw, who is
working as Geon-Woo's thug. The team immediately gets to work while complaining about the bad smell
caused by the sewer that runs under the hotel. There's tension among them because Dol-Yi thinks
he's better than everyone there, but at least he listens to Mr. Na's knowledge of the area to dig
in the right place. Meanwhile, Geon-Woo is dealing with a loan he took with his stocks as collateral.
He takes fifty million of company funds to buy low instead of paying what he owes because he's
sure there'll be an explosion soon that will allow them to sell high. Back to the team, they've made
a decent job in making the tunnel before they find their first problem: a deposit rich in lime. Its
moisture makes things dangerous, so Mr. Na wants to go around it. Dol-Yi thinks there's not enough
time for a new route, so they should just double the support and push forward. An argument ensues,
so Geun-Sab tries to calm everyone down by explaining they can zigzag the beams for
perfect support. While trying to demonstrate, he accidentally cuts a wire and hits Jeob-Sae,
who now wants to start a fight. Dol-Yi hits him and insults him, then raises Jeob-Sae's pants to
see the scarring and confirm he's the lowlife that tried to impersonate him. Feeling like he's won
the argument, Dol-Yi sends them all back to work. Mr. Na pauses to take some pills and Geun-Sab asks
him to share, but Mr. Na refuses because they're very expensive. After some more digging, they find
a rock wall at the end of the tunnel. It's not impossible to break, but doing so would make lots
of suspicious noises, so Dol-Yi tells Jeob-Sae to get noisy in the karaoke room to cover it up.
Meanwhile, Man-Sik and Sang-Goo are checking out all the abandoned buildings they can find. Man-Sik
finds the place where Dol-Yi did the drilling for Straw, and Sang-Goo goes to check the hotel,
getting surprised when he finds Counter because this building was supposed to be empty. Counter
explains they reopened recently while pressing the alarm, but because of the broken wire, the team
doesn't get the warning. She can't stop a cop from just looking around without raising suspicion,
so she waits for Sang-Goo to go down the corridor to contact the team through the walkie-talkies.
As the men begin to hide their work, Jeob-Sae distracts Sang-Goo long enough with his singing
that by the time the officer makes it to the basement, the team has covered the hole and is
pretending to do sewer work. Sang-Goo thinks he's seen Dol-Yi before, so he pretends he's been to
the station a few times to pick up Mr. Na when he got drunk. Not finding anything of interest,
Sang-Goo leaves, and Counter immediately goes down to fix the alarm wires. However, something goes
wrong and explodes, causing Counter and Geun-Sab to get trapped in the tunnel. Believing them to
be dead, Jeob-Sae wants to take the chance to get their advance money and escape, and Dol-Yi
wants to quit too because they've exposed a gas pipe. However, Mr. Na doesn't want to give up and
starts digging in case their coworkers are alive. This proves to be a good idea because Counter and
Geun-Sab are indeed alive and digging as well, so among the three of them, they manage to make
a hole to escape. In the meantime, Man-Sik has called back-up to show them what he's found.
His boss is quite impressed and finally accepts to send his men to scan the area and find the moles.
Sometime later, Dol-Yi hears the alarm and finds Jeob-Sae trying to run away with his money.
Dol-Yi catches him and begins kicking him for almost getting everyone in trouble, and Geun-Sab
joins the beating, but Mr. Na stops them from going too far. Jeob-Sae explains he has a sick
son that needs the money for his treatment, so Mr. Na tries to convince Dol-Yi to make an exception,
but that's when Dol-Yi realizes something. He goes to see Counter and confirms she was the one
that rang the alarm because there are cameras that keep an eye on everyone's moves - part of her job
is also to let their boss know if anyone breaks the rules. Speaking of the devil, Geon-Woo shows
up with Straw and his thugs to warn the team of the contract. Since nobody escaped in the end,
he accepts to give them a second chance, but now they have ten days to finish the job if
they want to keep their lives. Afterward, the thugs torture Jeob-Sae for trying to escape,
and Geon-Woo only lets him go after he accepts a deal: Jeob-Sae is given a secret phone,
and he must inform Geon-Woo of everything that happens while they work. If he does well, he'll
be paid extra one hundred thousand. The team goes back to work, and Mr. Na keeps taking his pills.
Since the others keep bothering him to share, he confesses they're for cancer.
Meanwhile, the police look for them using metal detectors, and when they finally get a response,
they begin digging with an excavator. Counter sees all this on the security cameras and rings
the alarm, so the team immediately starts taking out all the things from the tunnel. Dol-Yi goes
back to pick up a few metal things they forgot and is hit by a gas leak caused by the cops' digging,
cracking his ribs as he falls unconscious. Mr. Na refuses to leave him behind and puts on a mask to
rescue him while Counter checks on the police, who are now leaving because they've realized they're
messing with the gas pipes. Later, Mr. Na shares one of his painkillers with Dol-Yi and asks for a
favor: he wants to go to the hospital to check on his wife, who is having surgery today and it needs
to be paid for. Counter and Dol-Yi both refuse to risk the contract, but later in the evening,
Dol-Yi changes his mind. He takes his watch off and begins hammering the basement floor to access
the sewers and help Mr. Na reach the hospital in secret. Jeob-Sae finds them and calls them out
for their double standards, so Dol-Yi explains he can't compare himself to the last wish of a dying
man. Accepting this excuse, Jeob-Sae decides to go with them so he can ask a doctor to see his
burned leg. Counter also sees this escape on the security cameras, but instead of warning Geon-Woo,
she plays old recordings on loop. This trick seems to work because Geon-Woo doesn't suspect
anything when he checks the footage from his tablet, but Jeob-Sae ruins things by texting
him to let him know what's going on. Before Geon-Woo can leave for the hotel though,
he's visited by a loanshark that reminds him he needs to pay or his life will be in danger.
Geon-Woo simply answers by repeatedly hitting the man's head against the window. Back to the trio,
they make it to the sewers, and Mr. Na is surprised to find the old USA army sewer,
which is full of abandoned utility pipes. Eventually, they find a manhole and get out, but
by the time they make it to the hospital it's too late: Mr. Na's wife is already dead. Meanwhile,
a local woman calls the police because someone has been tossing construction trash in her garden,
and Sang-Goo recognizes it as pieces of the hotel floor. Man-Sik can't believe his partner believed
the sewer excuse and gets ready to investigate. At the hospital, Jeob-Sae decides to stay to get
his leg checked while Dol-Yi and Mr. Na go back to the hotel. Unfortunately, Geon-Woo, Straw,
and the thugs are waiting for them, and they've already captured Counter and Geun-Sab. Mr. Na
asks for mercy by explaining his wife's situation, but Geon-Woo doesn't listen and kicks Mr. Na.
Dol-Yi refuses to work with him any longer, but when he tries to leave,
Geon-Woo threatens him with hurting his mother. The team has no choice but to go back to digging
under Straw's supervision, and this time, Counter is sent to work with them as punishment.
Straw makes them work too hard without a break and soon Mr. Na is too sick to keep going,
but when Dol-Yi tries to defend him, Straw gets angry and a fight ensues. The team wins and tries
to leave to take Mr. Na to the hospital, but on their way out, Straw's men arrive to stop
them. Dol-Yi thinks quickly and grabs a gas tank and a welding machine to create a flame, getting
the thugs to stay away from them. Unfortunately, Geon-Woo also arrives and he's armed. Mr. Na tries
to jump on him to get the rifle, and in the struggle, an accidental shot kills him. Next,
Geon-Woo shoots Geun-Sab on the shoulder as a warning, and when Dol-Yi tries to attack him too,
he gets shot as well. At that moment, Man-Sik and Sang-Goo arrive at the hotel,
activating the alarm, so Geon-Woo and his men get away before they're caught. Once they're gone,
Dol-Yi opens his eyes, revealing the bullet hit the watch in his pocket instead of his body.
Between him and Counter, they help Geun-Sab up and escape together through the sewers. While waiting
for backup, Man-Sik finds the drill and is now more than ever sure that Drill-Bit is involved.
The trio makes it to Dae-Han's place, who has already sent Dol-Yi's mother to a safe hideout.
Counter explains that Geon-Woo is doing all this to pay a loanshark right before he calls the team
to threaten them again if they don't finish the job. Later, he calls Jeob-Sae at the hospital to
remind him to keep on passing information and warn him about the cops. It's too late though:
the officers have reached the hospital. Jeob-Sae gets to escape thanks to Dol-Yi, who shows up to
stop him from snitching on them and makes him rejoin the team to get revenge on Geon-Woo.
Now with the help of Dae-Han and his metal detector, Dol-Yi makes a plan using the utility
pipes Mr. Na had told them about to redirect the oil. First, Conter and Dol-Yi meet with Geon-Woo
to offer the oil in exchange for five million, and once they get Geon-Woo's ok, they begin to work.
They make a hole on the ground that Dae-Han covers with a container,
and Counter installs cameras on the sewer corridors while the men do the drilling.
Jeob-Sae takes a break as an excuse to meet with Straw and tell him what's going on. Not trusting
him, Dol-Yi follows him and sees him betraying the team, but he also discovers something bigger:
Man-Sik and Sang-Goo are in the area because they've been following their phones' signals.
In order to distract the cops, Dol-Yi runs into the woods to get them to chase him, getting hit
by a rock in the process, while Jeob-Sae goes back to the pipeline and installs a camera for Geon-Woo
to spy on them. After losing the officers, Dol-Yi goes back to the team and gets ready to finally
redirect the oil. Counter sees the cops show up in the sewers, but there's no time to stop the
drilling if they want to stay unnoticed by the oil company that keeps an eye on the pipe pressure.
The team decides to go for plan B, which consists of Geun-Sab and Dae-Han drilling a random wall
for the cops to see them and chase them out. The drilling goes well, but Dol-Yi is in too
much pain to keep working, so he guides Jeob-Sae to do the last step and finish the job together.
Dol-Yi opens the valve to send some oil to the tanks at the factory, where Geon-Woo has
gathered all his potential buyers. He opens a tap too and confirms the oil is there, so
Dol-Yi closes the valve and tells him on the phone he'll get access to the rest after getting paid.
Meanwhile, the cops' chase ends badly and Sang-Goo is sent to the hospital with a broken leg.
However, Man-Sik refuses to give up because someone sends him a picture of the new drilling
site. While Dol-Yi gets ready to receive Geon-Woo, Jeob-Sae betrays them again and opens the valves.
Dol-Yi catches him just in time and beats him up before tearing off the secret camera.
Counter, Geun-Sab, and Dae-Han also come back, and together they show Jeob-Sae
that Mr. Na had left his money for his son to make him feel shame for his betrayal.
After tying Jeob-Sae up, Dol-Yi meets with Geon-Woo and shows him how to use the valves.
However, instead of paying them, Geon-Woo calls his men to beat them up and get the oil for free.
Jeob-Sae escapes from his ropes and helps Dol-Yi beat up the men before he runs away. On the
surface, the other thugs enter the container at the same time, so Dae-Han uses a forklift to tip
the container over, allowing the team to leave the sewers and find the money. Dol-Yi stays a little
longer in the sewers, taking advantage of the rifle he's retrieved from one of the unconscious
thugs to threaten Geon-Woo. At that moment, they're found by Man-Sik, so Dol-Yi distracts
him by throwing the rifle at him and telling him to arrest Geon-Woo before running away too.
Unfortunately, when he joins his team, it's too late: Straw and his men have captured them all.
The thugs hit Dol-Yi too before taking him and the rest of the group to the pipe room, where they
discover Man-Sik has also been caught. Geon-Woo opens the valves to fill his tanks, then installs
a bomb as he explains his plan: there are bombs on the oil reservoir behind the water tanks too.
When he detonates them all, the pipeline will be busted and the country's main oil
reservoir will be out of commission, so Geon-Woo's company will be the only sellers in the market.
Such a huge explosion will also kill hundreds of people, but Geon-Woo doesn't care as long
as it gives him money, and it'll look like it's the fault of a mole heist gone wrong.
Desperate to escape, Dol-Yi makes the team kick over the welding machine, and with the help of
Counter's lighter, they start a fire that burns Dol-Yi's back but also burns the rope. Once he's
free, Dol-Yi grabs the bomb and throws it in one of the empty utility corridors before he jumps in
the sewer water so the explosion doesn't reach him. Geon-Woo detonates the bombs at the tanks
too, both to carry on his plan and kill Straw and his men so they don't snitch on him, but the
explosion isn't as big as he expects: in fact, the tanks only release water. It turns out that while
everyone was fighting, Jeob-Sae changed the valves and sent wastewater to the tanks instead of oil.
The team and Man-Sik leave the sewers, and the officer immediately calls for backup while they
watch the arrival of Geon-Woo and the thugs, who want revenge. Another fight ensues, and they use
anything available to defend themselves, from the forklift to an oil hose. Dol-Yi beats up Geon-Woo
and intends to kill him, but Man-Sik stops him from becoming a murderer instead of just a thief.
Man-Sik's backup arrives then and everyone gets arrested. Three years later,
the team has been freed on probation and is working in a shop of their own. However,
when Man-Sik comes to visit them, he finds them in the basement drilling a wall and doesn't believe
them when they say they're doing sewer work, so a new argument starts like the old days.