The good guys are having a hard time finding a lead for the current investigation. They find a possible culprit or a vital link in the investigation. The team gets an address and find the door slightly open.
This is a Death Trope so don't be surprised by spoilers behind the ominously open folders.
- In Arkham Asylum: A Serious House on Serious Earth, the parts that focus on the backstory of the founder, Dr. Arkham, has a scene where he walks into his house after finding the door wide open, calling for his wife and daughter. Guess what he finds.
- In The Ninth Gate, when Johnny Depp goes to the rare book store to retrieve the titular book he hits the doorbell only to find the door ajar. The store owner, his friend Bennie is found hanging by his heel, recreating the Hanged Man tarot card.
- In The Whole Nine Yards, when the detective knocks the door to find it open, he naturally takes out his gun to find several bodies that the tulip shot.
- Joked with in UHF. George Newman thinks open doors mean it's a friendly place. He isn't wrong, as he meets Philo, who will become a friend and essential ally against Channel 8.
- Towards the end of Blade Runner, Deckard returns to his apartment only to find the front door slightly ajar. He proceeds with caution only to find that it was Rachael who trespassed and is now sleeping in his bed.
- Logan is aroused when seeing the door to Gabriela's apartment ajar. Inside he finds her killed by the Reavers.
- A Door of Doom is found in Galaxy of Fear: Spore. When our heroes first see it it's locked, but when they come back...
- In Andre Norton's Catseye, Troy's return to Kyger's to find the door open puts him on high alert, though he has only minimal clues to what is going on. Turns out that Kyger was murdered, and Troy has to scramble.
- The YA novel A Deadly Game of Magic by Joan Lowery Nixon is somewhat unique in that the entire plot is centered around such a door—specifically, the four teen protagonists trying to avoid the killer magician trapped in the house with them as well as whatever Dark Secret he has left behind the door. And true to the trope, the answer turns out to be a murder: the old woman who owns the house (the magician's poor abused estranged wife), dead via guillotine.
- NUMB3RS is the trope namer, as seen in the first quote.
- Law & Order and all of its offspring live and breathe this trope.
- Subverted in the episode Profiteer. The cops find an ominously open motel door, one slowly opens it, dramatic music plays... and then the oblivious resident ambles up behind them with the bucket of ice he'd been getting.
- Pretty much any cop show has the cops in question reacting to the sight of an open door by drawing their weapons.
- Monk has a few variants.
- In "Mr. Monk Gets a New Shrink," Monk, Dr. Kroger and Harold Krenshaw end up finding the dead body of Dr. Kroger's cleaning lady in the shrink's office when they notice that the door to the office is slightly open.
- In "Mr. Monk Buys a House," Monk, Natalie, Stottlemeyer and Disher visit private nurse Cassie Drake's house, intending to get information from her on her killing of Joseph Moody. Unfortunately, "Honest" Jake Phillips has already stabbed and killed her to keep her from talking. Stottlemeyer and Disher try knocking on the door for about a minute, then Randy pulls on the knob and finds that the door is unlocked. They pull the door open and find the body.
- This is how Sebastian's Act 2 personal quest starts in Dragon Age II. When he goes to confront the people that had his family assassinated, he finds the door wide open with no guards in sight. "This is not the Lady Harimann I remember." Further inside, the Harimanns are all wildly hallucinating thanks to the Desire Demon their mother's been dealing with.
- In Justice League Unlimited - when Shadow Thief kidnaps John Stewart / Green Lantern, Vixen decides Carter Hall / "Hawkman", who's fought him before, might have a lead. She and Hawkgirl head to the museum where Carter works...only to find the door hanging open despite the "closed" sign.