The movie opens at a top secret laboratory in the Arctic Circle. Two men are playing cards, when suddenly, their coins are lifted into the air by a magnetic force. All the metal items around them are suddenly lifted high into the sky, and it is revealed that a giant aircraft shaped as a magnet is pulling everything. It lifts the entire laboratory off the ground and flies away with it. From elsewhere, a man watches the scene and tells a woman next to him to find whoever is responsible.
We catch up with Gru (Steve Carell), who is assembling what looks to be a pretty cool gun...until he uses it to inflate a unicorn balloon. He's throwing a birthday party for Agnes (Elsie Fisher), which has a fairies and unicorn theme. Edith (Dana Gaier) is hopping around dressed as a ninja while Margo (Miranda Cosgrove) and the minions are dressed as knights. Gru gets a call to learn that a woman he hired to play a fairy princess for the party is cancelling, so he has the minions stall. They put on a magic show that Margo stops when a minion holds a chainsaw close to Edith. Gru then comes down dressed as a fairy princess to enchant the kids. Agnes tells Gru she knows it's him but plays along for the kids and is still happy nonetheless. When she leaves, a guest named Jillian (Nasim Pedrad) pesters Gru about trying to set him up with one of her gawky friends. He responds by spraying her with a garden hose.
After the party, Gru takes his mutant dog Kyle to go pee. Unbeknownst to them, they're being watched. After Gru has Kyle pee on the neighbor's flowers (and rotting them with his toxic pee), a woman steps out and introduces herself as Agent Lucy Wilde (Kristen Wiig) of the Anti-Villain League. She orders Gru to go with her, and he responds by pulling out his FREEZE RAY! She deflects it with a flamethrowing hair dryer and zaps him with her LIPSTICK TASERRRRRRRR! She stuffs him in the trunk of her car and drives away as two minions (Dave and Carl) run after her to get Gru back. They end up falling into Lucy's car (and get zapped as well) before she drives off a pier and into the ocean as the car transforms into an underwater vehicle. She takes them all the way to a large submarine to meet with the Anti-Villain League and it's director Silas Ramsbottom (Steve Coogan). They keep a close eye on villainous activity going on over the world, so they were first alerted of the laboratory theft. Turns out that within the laboratory was a project for a serum known as PX41, and, as seen in a lab video, it is used for mutations. It is tested on a bunny that turns into a ferocious purple beast that kills a doctor. The League believes that traces of the serum lies within the Paradise Mall. Knowing Gru's past work as a villain, Silas and Lucy ask for his help but he rejects them in favor of his new life with the girls and an apparent business venture in jams and jellies. Before he leaves, Lucy admits that she found his past work to be awesome, so she gives him her card, and he is forced to row back home with Dave and Carl.
Gru goes home to tuck the girls in. He notices Margo is texting someone named Avery, and he hopes it's not a boy. Edith asks Gru if he will take Jillian's offer on going on a date with one of her friends and asks him if he's scared. This prompts a flashback in which Gru, as a child, nervously tries to talk to a girl, only for everybody to mock him as he taps her arm, saying he has "Gruties."
He goes to his lab where Dr. Nefario (Russell Brand) and the minions are working on a large batch of jelly. Dr. Nefario has managed to make a jelly with every berry in the world, and it apparently tastes terrible. He then admits to Gru that he misses doing villainous work and tells him that he's found work elsewhere. Dr. Nefario packs his things and leaves after Gru and the minions give him a "21 fart gun salute."
A minion dressed as a maid is passing the vacuum in the living room when he hears the doorbell ring. He answers it and screams as he is taken away.
The girls try to make a profile for Gru on a dating website. They can't find a good picture of him, and he stops them before they continue. He informs them that he has decided to help the League in their mission to finding the mystery villain. He goes to the Paradise Mall with Dave and Carl and they undercover at a cupcake store and finds that Lucy has been assigned as his partner. She appears very excited and eager, and they scope out suspects around the mall. Gru dismisses all of them until a pudgy little Mexican man named Eduardo Perez (Benjamin Bratt) strolls in. He says he works in a Mexican restaurant in the mall and that he is having a Cinco de Mayo party and orders hundreds of cupcakes with the Mexican flag. Before he leaves, Gru gets a good look at his face and recognizes him as an old villain known as El Macho. According to Gru, El Macho was, as the name suggests, incredibly tough, pulling off heists with his enormous strength. He apparently died in the most over-the-top way possible - namely, falling out of a plane while riding a shark that is strapped to a rocket and loaded with dynamite and is hurtling into a powerful volcano. Despite that, Gru adamantly believes the man they just saw was El Macho.
That night, before he tucks the girls in, Agnes asks Gru to help her practice a poem for Mother's Day. He does help her but she is totally robotic in her delivery. Gru tells her to pretend she has a mom, which she happily admits that she always pretends. The reality hits Gru that the girls need a mom.
The minions have an ice cream party in the lab as Gru goes to fetch Dave and another minion named Stuart. Upstairs, two minions are playing golf when they hear a commotion outside. It's just a cat, but then both minions are sucked up into the sky by a beam of light..
Gru and Lucy sneak into the mall to infiltrate Eduardo's restaurant. Lucy sprays something in the air to look for any alarms, but Gru doesn't believe there would be any in a restaurant until he trips a wire, alerting a guard chicken. He appears harmless until he starts pecking Gru in the face. Lucy then neutralizes the chicken so they can continue the mission. She gives Gru x-ray goggles to scope the place out. He sees a container locked in a safe behind a portrait, but when he opens it, it turns out to be a jar of salsa. They hear Eduardo coming in and he threatens to kill any intruders coming in. Gru calls for the minions to come get them, and they drive Lucy's car into the mall and help Gru and Lucy escape.
The next morning, the minions chase after an ice cream truck. While they try to place an order, the large ice cream cone on the top opens up and sucks all of them in.
Gru and Lucy go back to the mall hiding in garbage bins. She tells him that they have a suspect named Floyd Eagle-san (Ken Jeong) who works in a wig store. Gru tries to go in but tumbles down the escalator when someone tries to throw away hot coffee on him. He falls before the girls, who have come to hang out at the mall. They meet Lucy, and Agnes immediately assumes that Gru likes her and will marry her. Gru gives the girls money so they can go away while he continues the mission. The girls go to a fountain to throw coins (Edith actually steals them), and Margo spots a suave-looking boy named Antonio (Moises Arias). She is instantly smitten by him, and he goes up to her and invites her to get a cookie.
Gru goes into the wig shop to find the serum. Lucy informs him that the alarm on his belt will go off if it detects the serum. Floyd offers him a wig as Gru goes around the store, and the alarm goes off near one section of the store. He is interrupted with Edith and Agnes run in to tell Gru that Margo has a boyfriend. He quickly runs out and finds Margo and Antonio in Eduardo's restaurant sharing a plate of cookies. He tries to break them up as Eduardo comes in, doing a wild dance to entertain the guests. He introduces Antonio as his son and invites Gru and the girls to the Cinco de Mayo party, to which the girls are excited for, but Gru remains suspicious.
Gru and Lucy meet with Silas at the Anti-Villain League headquarters, where they still think Floyd is holding the serum, but Gru still firmly believes that Eduardo is El Macho, even though Silas does not think so.
One of the abducted minions wakes up on an island to find all the other minions playing and enjoying themselves on a beach. The minion takes off his pants and goes skinny-dipping. It is revealed they are being watched from a monitor by someone else.
Jillian goes back to Gru's home with her friend Shannon (Kristen Schaal). Gru tries to get Agnes to send her out, but he relents and uses a wig from Floyd's shop to go on the date. They go to a restaurant and it proves to be a mess since Shannon is totally unappealing and shallow. Lucy comes in to get take-out and she sees Gru on his date. When Shannon tries to remove his wig, Lucy shoots her in the butt with a moose tranquilizer. They take her home together and Gru feels a connection forming with Lucy. She kisses him on the cheek and leaves.
Gru wakes up the next morning, totally in love and feeling bright as ever, making heart-shaped pancakes for the girls and going around town interacting pleasantly with everybody. He goes to the mall to find that the wig shop is being investigated by the Anti-Villain League. They take Floyd into custody as Silas tells them Gru proved useless to them, since they found a container with traces of PX41 in the shop on their own, and they are also relocating Lucy to Australia. She bids him farewell and gives him her lipstick taser. He goes home depressed and miserable. He tells Agnes that he really does like Lucy, and then later tries to call her and ask her on a date, but he gets so nervous that he pulls out a flamethrower and incinerates his telephone. Cue the minions bursting in with an axe, fire extinguisher, and a hose.
The golfing minion (Kevin) is lounging on the beach, when he is sucked into a whirlpool. He reunites with the maid minion (Tom), but they are both injected by the PX41, which turns them into aggressive purple mutants.
Gru takes the girls to a bigger restaurant that Eduardo has outside the mall. He tries to get Margo and Antonio away from each other, but they dance anyway. He sits by himself with a large sombrero that is really a big nacho filled with guacamole. Eduardo comes in and knows Gru feels lovesick and tells him to enjoy the party as he strolls away suspiciously. Gru follows him and sees him enter a lair with a code that involves dancing to "La Cucaracha". Gru tries it but keeps messing up and nearly getting killed by the booby traps. He manages to make it in.
Meanwhile, Lucy is on a plane to Australia, but she can't get Gru out of her mind. The stewardess comes in, but all she can see is Gru, even with the other passengers. When the stewardess says she needs Lucy to make a decision, she declares "I choose Gru!" She proceeds to jump out the emergency exit and paraglides down back to Gru.
Gru enters the lair to discover that Eduardo really is El Macho, preparing to make the ultimate comeback. Additionally, Dr. Nefario is working with him, and he has helped Eduardo turn the minions into indestructible killing machines. He demonstrates by having Kevin come in and eat everything from a police car to a bomb. To top it off, he has an entire army of them. He asks Gru to join him in this villainous venture, but Gru refuses and leaves. Eduardo lets Kevin loose.
Gru goes to get the girls and finds Margo looking bummed out. She points out that Antonio is dancing with another girl. Gru takes her out, but not before freezing Antonio for breaking Margo's heart. After they leave, Lucy glides into the restaurant to find that the guard chicken is trying to attack her. Eduardo comes in and picks him up and realizes that Lucy and Gru had broken into the restaurant the other night. He takes Lucy with him as Dr. Nefario watches.
Upon returning home, Gru receives a video message from Dr. Nefario, who tells him that Eduardo has taken Lucy. Gru instantly springs into action, taking two minions with him on a motorcycle to rescue Lucy.
Evil Kevin makes his way to Gru's neighborhood and breaks into his home, trying to attack Margo and Agnes. When he tries to destroy Agnes's unicorn doll, she lets out an ear-piercing scream that distracts him long enough for the girls to make their way to Gru's lab. Evil Kevin makes his way down there quickly, but is then stuck with an antidote by Dr. Nefario, effectively turning him back into a normal minion. Dr. Nefario has the girls help him stick the antidote in all the jelly so they can head out and save the other minions.
Gru has his minions paint themselves purple and pretend to capture him to take him to Eduardo's restaurant lair. One minions gets into a raspberry-blowing match with a mutant minion, which causes the paint to wear off. Gru and the minions run and are chased to the top of the lair by the evil minions, but Dr. Nefario and the girls arrive in time to shoot the minions with the jelly antidote, turning all of them back to normal. Gru goes off to find Lucy, but discovers that Eduardo, dressed as El Macho, has strapped Lucy to a rocket and plans to kill her the same way he faked his death. Without his mutant minions, he drinks the last of the PX41 and transforms into a massive and hairy purple beast that tries to attack Gru. He is out of the jelly antidote and tries to shoot his freeze ray at him but he is too powerful. Gru then takes out Lucy's lipstick taser and zaps Eduardo, bringing him down. Dr. Nefario finally knocks him out with a fart gun, and they presumably change him back with their own jelly antidote.
Gru goes to save Lucy, but Eduardo's chicken presses the button to launch the rocket into the volcano. Gru cuts Lucy free, but before he can get them away from the volcano, he asks her if she would have ever agreed to going on a date with him. She enthusiastically replies that she definitely would have, and he jumps with her into the ocean before the rocket hits the volcano and explodes.
147 dates later, Gru and Lucy get married. Agnes recites her poem with confidence and calls Lucy her new mom. She jumps into her arms, and the minions begin to perform their own rendition of "YMCA". They take pictures with everybody, including Silas and Gru's mom. The film closes as one forgotten evil minion jumps into a picture.
During the credits, the minions hold auditions for their upcoming spin-off film, but are continuously cut off by the credits.
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