The film follows Mike Enslin, an author who specializes in the horror genre. Enslin's career is essentially based on investigating allegedly haunted houses, although his repeatedly unfruitful studies have left him disillusioned and pessimistic. Through an anonymous recommendation (via postcard), Enslin eventually learns of the Dolphin Hotel in New York City, which houses the infamous "Room 1408". Interested yet skeptical, Enslin decides to spend one night in the hotel although manager Mr. Olin warns him strongly against it. Enslin encounters a series of bizarre experiences in the room.

Mike Enslin (John Cusack) is a skeptic author who debunks supernatural occurrences after the untimely death of his daughter Katie. He rates supernatural places with 'skulls' on a scale of 1 to 10 based on the unnerving atmosphere and scariness of the location. Before this event he used to write fiction, and a woman at a book signing asks him to sign a copy of his first book, a novel called The Long Road Home. After finishing his latest successful book, he receives an anonymous postcard of the Dolphin Hotel in New York City bearing the message "don't enter 1408". Viewing this as a challenge, Enslin attempts to book a reservation for room 1408, but the hotel will not rent him the room. However, after being informed by Enslin's agent Sam Farrell (Tony Shalhoub) that the Fair Housing Act requires hotels to rent unoccupied rooms, the Dolphin reluctantly reserves room 1408 for Enslin. Arriving at the Dolphin, Enslin is pulled aside by the hotel's manager, Gerald Olin (Samuel L. Jackson), who warns him that no one has lasted more than an hour in 1408. Olin tries to be friendly with Enslin; he compliments him on The Long Road Home, offers Enslin an upgrade to the penthouse suite, an $800 bottle of cognac and access to documents regarding the deaths in 1408 if Enslin abandons his plan to stay in the room. When Enslin insists, Olin begins reciting the docket of carnage that includes seven jumpers, four overdoses, five hangings, three mutilations, two stranglings, one drowning and twenty-two natural deaths in room 1408. Enslin accepts the documents and the cognac but insists on staying in the room, frustrating Olin.

Once inside the room, Enslin pulls out his Mini Cassette recorder and dictates on the unremarkability of room 1408. As he examines the room, the clock radio suddenly starts blaring "We've Only Just Begun" by The Carpenters, and chocolates appear on the bed pillows; he is startled, but dismisses these things as gags cooked up by Olin. When he calls for room service, the hotel operator agrees to random requests Enslin didn't make such as ordering a sandwich, substituting side dishes, and dry cleaning. Later, Enslin is startled again as the clock radio begins to play the same previous song. The clock's digital display scrambles to 60:00, and then starts counting down from 60 minutes. When he rips the clock's electrical cord from the wall, it continues to tick down. Suddenly, Enslin is unable to hear anything, apart from a tinnitus-like ringing in his ears, and opens the window to check his hearing. The window slams down, cutting a large gash in the top of his hand. Enslin attempts to treat his hand and escape the room, but his attempts are cut off - the key and then the doorknob to the door break off, and he cannot break it down.

Enslin begins to see and hear things, including visions of other victims and the room, and of his daughter and his wife, but he initially dismisses them as hallucinations, possibly due to a drug in the cognac or chocolates. He makes several attempts to free himself from the room, such as trying to crawl outside on the ledge to the next room or crawling through the air vents, but logic-defying events prevent him from succeeding, all the while being assaulted by horrifying illusions. Several times, he has illusions about his family traumas: he encounters his late, invalid father in a hospital room (whom he may have alluded to when he described a plot element of The Long Road Home), and continues to see visions of Katie. Finally, Mike manages to contact his estranged wife Lily (Mary McCormack) via video chat and begs for help, but the conversation ends abruptly when the sprinkler system shorts out his laptop. All the while the room temperature drops, eventually to subzero temperatures.

Mike's laptop starts working again and he hears Lily calling out to him via video chat, but a doppelgänger of him hijacks the conversation, urging Lily to come to the hotel immediately and enter room 1408. As Enslin desperately tries to tell his wife not to come, the room begins to shake violently, and water explodes and floods out of a painting of a schooner lost at sea, pulling Enslin under the surface. Enslin wakes up on the beach, the result of a surfing accident depicted earlier in the film. He soon finds Lily at his bedside in a hospital near his home in Los Angeles; she tells him that he was hospitalized after sustaining a concussion, leading him to conclude 1408 was just a dream. This reprieve is short-lived, however, when at the post office to mail a manuscript of his latest book (with a story about 1408) to his agent, a construction crew made up of hotel staff and guests begin to destroy the interior, revealing the walls and floor of 1408 underneath, now severely fire-damaged; he is still trapped inside 1408.

Enslin encounters his dead daughter, but as he emotionally embraces her she dies in his arms, then crumbles to dust as the clock radio's countdown approaches zero. Enraged, Enslin lashes out against what remains of the room until he falls to the floor, exhausted. When the clock radio finally reaches zero, the room changes back to its original, undamaged appearance, and Enslin's wound miraculously heals. The clock radio resets for another 60 minutes and the phone rings; when Enslin answers, the friendly female voice of the hotel operator informs him that he can relive the hour "again and again" or choose to take advantage of their "express checkout system". A noose appears in the bedroom and Enslin has a vision of him hanging himself; he tells the operator that he will not be checking out that way. The phone rings again, and the operator reminds him that his wife will be arriving in 5 minutes and will be sent right up to his room. Deciding to end it at last, Mike turns the cognac into a Molotov cocktail and sets the room on fire, causing the hotel to be evacuated. Lily arrives just seconds afterwards and is stopped from entering the hotel, but tells the firefighters that Enslin is in 1408.

Meanwhile, as the room tries to extinguish the fire, Enslin proudly awards the Dolphin Hotel 10 Skulls, as he breaks a window with an ashtray, causing a huge backdraft that engulfs 1408. The firefighters force entry into the room and rescue Enslin as he curls under the coffee-table, delighted that the room is dying. Enslin recovers in a New York hospital, Lily at his bedside. He swears that he saw Katie, but Lily refuses to believe him. After his recovery, Enslin is seen moving back in with Lily, beginning work on a new novel that has nothing to do with his previous cheap haunted sites series. While sorting through a box of items from his night in 1408, Enslin comes across his mini cassette recorder. After some difficulty he manages to get the tape to play; it begins with Enslin's dictation of 1408's appearance, but cuts in with audio from his interaction with the apparition of his daughter. Lily freezes in shock as she hears her dead daughter's voice coming from the tape recorder, and the film closes on Enslin meeting her shocked stare with one of grim vindication.

Alternative ending

Director Mikael Håfström has stated that the ending for 1408 was reshot because test audiences felt that the original ending was too much of a "downer".^[2] The original ending, available exclusively on the Director's Cut edition, sees the backdraft engulfing the room as Enslin hides under the coffee table, happy to see the room destroyed as he dies. Olin later approaches Lily and Enslin's agent at his funeral, where he unsuccessfully attempts to give back a box of Enslin's possessions, telling her, relieved, that Enslin did not die in vain. Olin listens to the recording in his car, hearing Katie's voice on the tape; he jumps in surprise as he catches a quick glimpse of the now horribly burnt Enslin in his rear view mirror. Enslin now bears resemblance to a ghostly man that appeared in several other scenes, including the window/mirror scene and in the painting of the schooner. The scene then changes to an outside view of the gutted 1408, with an apparition of Enslin disappearing after being called away by the voice of his daughter and the sound of a closing door.

The UK and Irish rental DVD is branded as the "Director's Cut" and therefore includes the original ending. The director's commentary on both the DVD and the special features on the DVD contained no references or hints towards the ending in which Enslin lives or any explanation as to why the ending has been changed. Most, if not all, theatres originally showed the film with the ending in which he does live.

In the Blockbuster version of the DVD, there are 2 other alternate endings, in one of them, Michael Enslin ends up dying in room 1408, as his publisher and widow are cleaning his apartment in California, the publisher expresses his sorrow and leaves to New York. As the Publisher is entering his office he gets the mail from his secretary, as he looks through all his mail he notices the last envelope, which is from Michael Enslin, the same envelope he tried to send in his supposed awakening in the middle of the movie, the envelope contained a finished novel of his experience titled "1408".

The next version is mostly the same as the original ending except Michael's wife does not hear the recording of Katie as she is in the kitchen cleaning, leaving Michael to experience the moment by himself.

• John Cusack as Mike Enslin
• Samuel L. Jackson as Gerald Olin
• Mary McCormack as Lily Enslin
• Tony Shalhoub as Sam Farrell
• Len Cariou as Mike's Father
• Jasmine Jessica Anthony as Katie Enslin