Here's a little synopsis for those of you who never read the short story nor saw the trailer:
Warning: Significant plot details follow.
As in many of King's works, the protagonist of the story is a writer, in this case Mike Enslin, who writes non-fiction works based around the theme of haunted places. His book series, Ten Nights in Ten Haunted Houses, Ten Nights in Ten Haunted Graveyards, and Ten Nights in Ten Haunted Castles, prove to be bestsellers, but Enslin internally reveals some guilt and regret at their success, privately acknowledging that he is neither a believer in the occult nor in the supernatural elements he espouses in these books. Nonetheless, he arrives at the Hotel Dolphin on Sixty-first street in New York City intent on spending the night in the hotel's infamous room 1408, as part of his research for his next book, Ten Nights in Ten Haunted Hotel Rooms. At first Enslin is unfazed by 1408's morbid history; according to the hotel's manager, Mr. Olin (who has purposely left it vacant for over 20 years) room 1408 has been responsible for 12 suicides and 30 natural deaths over a span of 68 years. While remarking that he doesn't believe there are ghosts in 1408, Olin insists there is "something" that resides inside, something that causes terrible things to happen to people who stay within its walls for anything but the briefest periods of time, something that affects various electronic devices, causing digital wristwatches, pocket calculators, and cell phones to not function or to operate unpredictably. Mr. Olin also reveals that, due to the superstitious practice of never recognizing the 13th floor, the room is listed on the 14th--it is a room cursed by existing on the 13th floor, the room numbers adding up to 13, making it all the worse; he pleads with Enslin to reconsider, believing that a skeptic such as he is even more susceptible to the room's curse. Enslin is shaken but his determination to follow through with his research, and to not appear frightened before Mr. Olin, wins out. Olin reluctantly leads him to the 14th floor, unwilling to accompany him farther than the elevator.
Enslin's problems with Room 1408 begin before he even sets foot through the door; in fact, the door itself initially appears to be crooked. He looks again and the door appears to be straight - then again, and it appears to be crooked again (though this time leaning to the left instead of the right).
As Enslin enters and examines the room, and begins dictating into a hand-held tape recorder, his train of thought immediately takes unwelcome and chaotic turns - he compares it to "being stoned on bad, cheap dope". He begins experiencing what may or may not be hallucinations; the breakfast menu on the nightstand changes languages and finally turns into a woodcut of a boy being eaten alive by a wolf, pictures on the walls shift into disgusting perversions, and Enslin's thoughts become bizarre and incoherent.
Panicking, Enslin tries calling the hotel operator but instead hears an inhuman, rasping voice coming from the phone's receiver, incessantly reciting numbers: "This is nine! Nine! This is ten! Ten! We have killed your friends! Every friend is now dead! This is six! Six!"
Enslin watches with horror as the room seems to melt before his eyes, and he senses a hungry, inhuman presence approaching. He can't seem to keep a clear head long enough to walk to the other side of the room. He opens a book of matches and, in a last-ditch effort to shock himself back to awareness and clear his perceptions, sets his shirt on fire. Engulfed in flames, he manages to escape the room, bursting into the hallway just as another guest happens to be walking by with a bucket of ice; the guest extinguishes the flames and saves Enslin's life, though he will suffer health problems, paranoia, and severe nightmares from that day forward. Traumatized, Enslin quits his lucrative career (to the dismay of his agent) and retires to a beachhouse, completely shut off from society, the disturbing tape recording becoming the only testament of his ordeal. The story ends with Enslin muttering to himself about the inhuman nature of 1408 ("It was never human....At least ghosts were once human. That thing in the wall, though... that thing...")