The plot follows a bullied 12-year-old boy who befriends and develops a romantic relationship with a child vampire girl in Los Alamos, New Mexico, during the early 1980s.

Interest in producing an English-language version of Let the Right One In began in 2007, shortly before the Swedish film was released.

Reeves made several changes for the English version, such as altering the setting from Stockholm to Los Alamos and renaming the lead characters.

The film's producers stated that their intent was to keep the plot similar to the original, yet make it more accessible to a wider audience.

While the detective answers a call outside the room, the disfigured man jumps out of the window, leaving behind a note that reads: "I'M SORY ABBY".

Two weeks earlier, Owen, an unhappy and lonely 12-year-old boy who is neglected by his divorcing parents, sees a barefoot little girl named Abby and an older man moving in next door.

At school, a teenage bully named Kenny and two of his friends constantly terrorize Owen, who lies to his mother about it but tells Abby the truth.

Abby's companion Thomas abducts a local teenager and drains the boy's blood into a jug, only to accidentally spill all of its contents.

Cornered by the bullies, Owen smashes the side of Kenny’s head with a metal pole, splitting his left ear.

According to Hammer Films executive producer Nigel Sinclair, interest in the project initially began in the middle of 2007, before the original Let the Right One In had screened for audiences.

[23]In adapting the film, a few adjustments were made, such as changing the names of the protagonists to Owen and Abby,[24] and moving the setting from the Stockholm suburb of Blackeberg to "a small New Mexico town.

"[23] The filmmakers have noted that "they intend to forge a unique identity for Let Me In, placing it firmly in an American context", while at the same time paying respect to the original.

[25] In comparing his adaptation to the Swedish one, Reeves admitted to not adding many different details from the book that weren't in the original film, stating that "the story was so big that you couldn't really add a lot of stuff in without taking away the focus of the coming of age story so I tried to have allusions and references to stuff in the book."

"[23] In adapting the story for American audiences, Reeves stated that keeping the 1980s time period within the film was critical in exploring the theme of good and evil.

Reeves felt that this idea was central to the main character Owen, as he "would be grappling with these very, very dark feelings but being in a kind of American town where there was that sort of [Reagan era] mindset and religiousness.

[28] The casting of Moretz and Smit-McPhee in the leading roles was confirmed on October 1, 2009, along with the addition of Richard Jenkins as Abby's adult companion.

[29] In a press release, director Matt Reeves described Smit-McPhee, Moretz and Jenkins as his "absolute dream cast", and added that he "couldn't be more excited to be working with them.

"[30] Both Smit-McPhee and Moretz were cast before the release of The Road or Kick-Ass, and the films' directors John Hillcoat and Matthew Vaughn, respectively, each praised the young actors and recommended them to Reeves.

Faden noted the techniques used in another challenging shot important to Abby's character in which she begins bleeding when she enters Owen's apartment without invitation.

Then using techniques utilized in a prior Method Studios film, A Nightmare on Elm Street, Faden had the Houdini software track Moretz's shaking movements and render the gradual release of blood from her face.

Composing the score to convey the correct emotion was also a challenge for Giacchino who said, "... it was tricky finding the right balance of, well, should this be scary?

The consensus is that "similar to the original in all the right ways—but with enough changes to stand on its own—Let Me In is the rare Hollywood remake that doesn't add insult to inspiration.

"[56] Joe Morgenstern of The Wall Street Journal wrote that the film "is more than a respectful remake; Let Me In is quietly stylish and thoroughly chilling in its own right.

Josh Tyler of CinemaBlend wrote, "The movie he's made is absolutely a direct remake of the 2008 film, the two are so similar that it's almost impossible to differentiate between them.

"[62] In a similar vein, Jamie S. Rich of DVD Talk noted that while there was plenty of content in the original novel that the Swedish film omitted, "Reeves hasn't really ferreted out anything new; on the contrary, there is actually less plot in Let Me In than in the Alfredson version.

"[66] Let Me In was a critics' pick as one of the Top 10 Best Films of 2010 at CNN[67] and at MSN Entertainment for the 2010 Year in Review Special Features.

John Ajvide Lindqvist, author of the book and screenwriter of the original Swedish film, was pleased with Let Me In.

The first issue has Abby and her "guardian" facing a ruthless real-estate tycoon who wants to steal their home and was released in December 2010.

[89] John Ajvide Lindqvist, who wrote the original novel that both the Swedish and American films are based upon, said "Nobody has asked me about [doing a comic] and I think that the project stinks.

"[90] Later, he informed fans that he had in fact unwittingly sold the rights for the comic to be made, stating that the producers had misinformed him as to the nature of the contract he had signed.