In the start of the films the Longlegs character is only seen from the neck down to heighten the suspense and his full first-time appearance is the undisputed high point of the film. This is surely the most memorable makeup job of the year, Cage’s costar Monroe said in an interview "when I first laid eyes on him, my heart leapt to an amazing 170 bpm".

Cage wearing heavy white facial makeup plays Longlegs, who looks like a crazy homicidal mock glam rocker who is sexually ambiguous. He resembles and parodies the look of the late, great singer from T Rex, Marc Bolan, who is a recent Rock and Roll of Fame inductee. The film invites us to compare the rock star to the Longlegs because the film constantly alludes to Bolan. One of the film’s characters has a poster up of Bolan (wearing his top hat in an image from the album, Slider) and the film contains several T Rex songs on the soundtrack. The screenplay writer/director Perkins has said that he listened to T Rex nonstop while he was writing the screenplay after Nicholas Cage brought the band to his attention.

The film even opens with the song, "Get It On (Bang a Gong)," as we see a title card with the following lyrics from a 1971 track: "Well you’re slim and you’re weak / You’ve got the teeth of the hydra upon you / You’re dirty, sweet, and you’re my girl." This song directly ties into the film because like the girl in the song, the lead female character’s life has been marked or altered forever by a mythological monster.

Longlegs is about a series of mysterious murders spread out over decades that are somehow connected. In each case a family is slaughtered by stabbing or shooting by a formerly normal dad who suddenly goes berserk and kills himself after he massacres his family.

Agent Harker (Maika Monroe who is quite convincing) is assigned the case by the FBI, and she is as strong or smart as the Jodi Foster character in Silence of the Lambs or the X-Files’ Agent Mulder whom she is obviously modeled after. Harker was able to catch her first killer right off the bat because she utilized some psychic abilities that come in handy in this film.

The agent suspects that the crimes are connected because in each case the killer leaves a note covered in ancient arcane mystical symbols. She also discovers that every family has a young girl who was born on the 4rth day of the month and the murders all occur within six days of her birthday.

One day Agent Harker is researching the case at her home when she hears a sinister laugh. She finds a note inside that has the same kind of mystical symbols that were found near the slaughtered families. The note is signed Longlegs and this is the start of a cat and mouse game between the killer and the FBI agent, and they built a relationship with each other similar to the killer and agent in Silence of the Lambs which featured Hannibal Lecter (the character Trump has been citing in his speeches).

We also get to meet Agent Harker’s half-crazy mom who has some connection to the killer. Despite her madness she is slightly sympathetic because she is completely devoted to her daughter and will do anything to keep her alive. Once the mystery is solved, we find out the Agent’s mom is involved in the mystery along with Longlegs.

In addition to three T Rex songs, the soundtrack contains many moody instrumentals created by the film director’s brother, Elvis Perkins, who believe it or not is the son of Anthony Perkins, the star of Psycho. Some of the music in the film is played backward to create a hypnotic effect on the audience.