After a break-up with a boyfriend, an overcautious Jen (Katherine Heigl) travels to Nice, France, with her parents (Tom Selleck and Catherine O'Hara). After getting into an elevator to go to her hotel room, she meets Spencer Aimes (Ashton Kutcher). Spencer asks her out for drinks, and she accepts. The scene then changes to Spencer sneaking onto a boat, putting a remote controlled bomb on the bottom of a helicopter, then taking out a guard. He then swims back and goes on the date with Jen. After the helicopter takes off, Spencer triggers the bomb using his phone.
After a night of drinking, Jen reveals that she is not the spontaneous person she's been pretending to be and, in return, Spencer bluntly tells her that he's an assassin, albeit unhappy about being one. Unfortunately, she's already passed out and hasn't heard. In spite of this, Spencer decides that Jen's the woman he's been looking for and decides to marry her. When Spencer tells his boss, Holbrook (Martin Mull), his plan, the response is that quitting is not an option. Spencer is defiant and goes ahead with his plan.
Three years later, they are settled into their new normal life. After Spencer surprises Jen with a remodeled office, she gives him a birthday surprise: tickets to Nice to celebrate his birthday and their three years. Because of his dubious connections to Nice, Spencer is less than enthusiastic. When Jen's friends ask about his reaction, they take it as a sign that he might be getting bored and fill her head with doubts.
Meanwhile, Spencer gets a postcard from his old boss and the ultimatum to take another assignment. While trying to refuse him long distance, Jen's father shows up to take Spencer to dinner, so Spencer hangs up the phone, prompting suspicion in Mr. Kornfeldt. This is fueled further when Jen's dad sees the postcard and quizzes him about the XOXX (hugs and kisses), being odd coming from a former boss. Stopping home to change, Spencer finds that the dinner invitation is just a detour to bring him to a surprise party. While Spencer navigates drunken friends, Jen's friends continue to fill her head with doubts over Spencer's lack of enthusiasm for the Nice trip. This is further irritated, when the following morning, despite her attempts to be physical with him, Spencer rushes Jen off on her business trip.
A little while later, Jen comes back (without having gone on her trip) to find Spencer being tossed around their house by Henry (Rob Riggle), Spencer's best friend and co-worker. Spencer screams for her to get his gun (of which she was unaware) and she shoots Henry in the arm. While interrogating him, Henry reveals that there is a $20 million bounty on Spencer's head. An unidentified sniper takes shots at them, and Spencer and Jen flee. Henry goes after them; and, after a car chase through the neighborhood, they end up in a construction zone, where Henry crashes his car. Spencer rams him into a trench, impaling his car on rebar and killing him. They then go to the hotel room where Spencer's old boss is staying but find that someone has already killed him. Jen demands that they go to her Dad for help, but Spencer disagrees. In the middle of their argument Jen vomits and declares that she might be pregnant.
Heading back to his office for Jen to take a pregnancy test, Spencer is attacked by his secretary (Katheryn Winnick) and realizes that there are others who know about the contract. Jen then reveals that she is pregnant and is leaving Spencer. Left alone, Spencer is attacked by a delivery driver, who is then run over and killed by Olivia (Lisa Ann Walter), Henry's wife, another killer vying for the contract. She then tries to run over Spencer, but Jen returns and smashes Olivia's car into a fuel tank, which Spencer then shoots at and explodes, killing Olivia. The two discuss their possible future and return to their neighborhood, which is holding its annual block party. When they first arrive, they are attacked by two more assailants who, in a chase through backyards, crash their car, giving Jen and Spencer a chance to flee into the block party. As they walk through it, they receive many suspicious looks from neighbors. They enter their house to retrieve guns and their passports. Spencer is grabbing the guns when he is attacked by the two assailants again, whom he eventually kills.
Meanwhile, one assassin, Kristen (Casey Wilson), one of Jen's best friends, holds Jen's mother as a hostage in a Mexican standoff with Jen. Jen's father arrives and kills Kristen. He then explains that he was the one who put out the bounty on Spencer. He knew of Spencer's previous work all along, and hired the neighbors and co-workers three years before, in case Spencer started working for his old boss again, who Jen's father says had "gone dirty." After seeing the postcard from Holbrook in Spencer's office, he came to the conclusion that Spencer had re-accepted his old job and activated the assassins. He reveals that he had been an operative as well, and that he was actually the target Spencer was supposed to kill in Nice three years earlier.
In a standoff between Spencer and Jen's father, he does not trust that Spencer is really out of the game. Wanting to prove that he really did get out, Spencer drops his gun, and tells Jen's father he has no intention of killing him. Jen, now convinced, reveals her pregnancy to her parents. Jen's father, after killing one last wounded assassin, drops his gun as well. The family makes peace by building a trust circle, in which Spencer reveals that English is not his first language, and that he wanted to be the first one to say "I love you" to Jen. The movie ends showing Spencer and Jen's father working on some wires near Spencer and Jen's baby's crib. Spencer has grown a moustache just like Jen's father. Spencer and Jen then leave to let Jen's mom and dad babysit. They all leave the room, but Spencer comes back in to activate the lasers protecting the baby.Ashton Kutcher as Spencer Aimes
Katherine Heigl as Jennifer "Jen" Kornfeldt
Tom Selleck as Mr. Kornfeldt, Jen's father
Catherine O'Hara as Mrs. Kornfeldt, Jen's mother
Katheryn Winnick as Vivian, Spencer's secretary
Lisa Ann Walter as Olivia, Henry's wife
Casey Wilson as Kristen, Jen's best friend
Rob Riggle as Henry, Spencer's friend and co-worker
Martin Mull as Holbrook, Spencer's boss
Kevin Sussman as Mac Bailey, one of Jen and Spencer's neighbors
Alex Borstein as Lily Bailey, one of Jen and Spencer's neighbors
LeToya Luckett as Amanda, one of Jen's friends
Mary Birdsong as Jackie Vallero, Jen and Spencer's next door neighbor
Usher Raymond as Kevin, manager at K-Mart (cameo)
Filming began in the fall of 2009 and took place in the Tributary community in Douglasville, Georgia, Nassau and Villefranche-sur-Mer doubling for Nice.
The DVD and Blu-ray of the film was released on September 7, 2010.
Killers received generally negative reviews from critics. On Rotten Tomatoes, the film has an approval rating of 10% based on 106 reviews with an average rating of 3.3/10. The site's critical consensus reads, "Dull, formulaic, and chemistry-free, Killers is an action/comedy that's largely bereft of thrills or laughs." On Metacritic, the film has a score of 21 out of 100 based on 22 critics, indicating "generally unfavorable reviews". Audiences polled by CinemaScore gave the film an average grade of "B" on an A+ to F scale.
Ashton Kutcher "won" the Golden Raspberry Award for Worst Actor for his performance in the movie (also for Valentine's Day).
The film debuted at #3 at the box office behind Shrek Forever After and Get Him to the Greek, with an estimated $15.8 million in its opening weekend. Based on a budget of $75 million, Killers took in only $47 million domestically in the United States. With an additional $51.1 million overseas, the film grossed $98.1 million worldwide.