Suppose you have something that you really need to get to another person without other people knowing—maybe you're a spy with important information, maybe you're a police informant with a piece of incriminating evidence, maybe you're a government agent paying off an asset in foreign territory. Your phone might be tapped, you can't leave the country, and you absolutely cannot walk up to the authorities' door, suitcase in hand. What do you do?
A "dead drop" is one option. The gist of it is that there is a location, typically Hidden in Plain Sight, where one person can leave a message (or money, or just about anything that can fit in the container), then leave. Later on, someone else goes to the location and retrieves whatever was left at the drop. This allows for information or items to be exchanged without public interaction between the participants, which helps with Plausible Deniability: If the people in question never publicly (or even privately) associate, it's harder to prove any sort of connection between them.
The obvious risk is that someone can (inadvertently or otherwise) find the message. In fiction, if the protagonist happens to find a dead drop that isn't meant for him, the party that set up the drop will often try to do one of two things: Welcome him into the fold or try to eliminate him.
- In The Thomas Crown Affair (1968), the people who actually carry out the bank robbery, who are never allowed to see the mastermind's face, drop the stolen money off in a trash container at Cambridge Cemetery.
- In the Fritz Lang spy movie Ministry of Fear (1944), the Allied plans for the invasion of occupied Europe have been microfilmed by Nazi spies and hidden in a cake being raffled at a village fair. The next chain in the spy ring was supposed to 'win' the cake and take it with him, but by a fluke the protagonist gets it instead, setting off the plot. There's a Brick Joke at the end of the movie when the protagonist reacts in alarm when his Love Interest starts discussing their wedding preparations, which of course would include a cake...
- In Next Breed of Thief, this is the typical communication method between Elsha and Fireboy—the usual implementation is a false rock placed along a jogging route, though Fireboy also uses a potted plant.
- Discussed and averted in The Cardinal of the Kremlin: The chain of handoffs between "Cardinal"—a high ranking Soviet official who provides intelligence to the US—and the CIA's Chief of Station in Moscow has no dead drops. It's acknowledged that this bears the risk that the KGB could "pull the thread" by working their way back through the handoffs, but the information that Cardinal provides is too sensitive to be left in a dead drop.
- John le Carré's spy thrillers routinely detail how dead drops are conducted, as well as "color coding" to identify the contact and whether or not it's safe to make the drop / pick-up. Tinker, Tailor, Soldier, Spy has a dead drop occur on a ferry boat, with a yellow thumbtack acting as the "it's on" signal.
- In the book Cauldron of Ghosts, Victor Cachat re-establishes contact with seccy allies from the previous novel by spending a day checking assorted dead drops, then leaving a return message at one of them.
- In Aquarium, it is described that for most spies under diplomatic cover, all their work consists of either checking and filling Dead Drops, or driving around so that the police won't be able to pinpoint these. Actual contacts with agents are to be made as few as possible.
- The Fourth Protocol. A British politician suspected of stealing secrets makes his way across London to visit an ice cream store. The MI-5 Watchers are forced to follow every delivery to see who he's making contact with. One of the recipients is a diplomat in the South African embassy, who later makes a wrong number call to the ice cream store. The protagonist has a computer expert work out the odds of this happening by coincidence, which turn out to be astronomical. In the movie a pizzeria is used, and Michael Caine's character gets suspicious when the manager personally hands a pizza box to the man who turns out to be the South African diplomat.
- Several of Frederick Forsyth's other books also had the characters utilizing dead drops.
- A dead drop is often how Mission: Impossible agent Jim Phelps received the tape recorder and photographs that detailed his newest mission. Drop points have included a cathedral, a public fountain and a museum.
- In the TV movie Family of Spies: The Walker Spy Ring, John Walker's ex-wife tips off the FBI that her husband is selling naval secrets to the KGB. They don't believe her at first because she appears to be motivated by revenge, but analysts report that her description of the signals used to inform that a dead drop has been filled match those techniques used by the KGB.
- The Equalizer. In one episode, an innocent bystander is mistaken for the next link in a courier line of spies. A package was dropped off to the doorman of his apartment (the real courier). When someone turns up to murder the doorman and steal the package, he hastily scribbled an address on it to make it look like normal mail. Unfortunately the killer was not fooled and stole the package, assuming that the address was for the next link in the chain which he was trying to shut down.
- At the start of the third season of Battlestar Galactica (2003) the resistance are receiving information this way from a source inside the Cylon government. Information is left inside a filing cabinet and a nearby dog bowl is flipped over to indicate a delivery has been made. Tyrol, who collects the information, doesn't know who's making the deliveries and explains that it's safer for everyone that way. The audience quickly learns that it's Gaeta, President Baltar's aide, who's been making the drops. Once the Cylon occupation has been dealt with Gaeta reveals he was the source by describing the drop method in front of Tyrol, information that saves him from being executed as one of Les Collaborateurs.
- The spies in The Americans often use these; one mark is a yellow chalk line on a mail box.
- A system of dead drops is used by the Dark Brotherhood in The Elder Scrolls IV: Oblivion to assign new assassination contracts and to transfer payments to you. Half-way through the quest line, however, it is hijacked by a traitor and you are instead sent to assassinate the entire Brotherhood leadership.
- In PAYDAY 2, players can request dead drops of supplies during heists to aid them. With the introduction of the Dentist, it's now possible to strategically place the drops in different locations on some heists.
- In Fallout 4, dead drops are how members of The Railroad, a group of rebels who help Synths escape The Institute and get new lives, communicate and get their assignments. In their case, it's not so much for plausible deniability (since the wasteland of the Commonwealth has no real ruling government) but survival. The Institute can teleport an army of Synths, or worse, Coursers, directly to The Railroad's hideouts the instant they know where they are. Thus The Railroad has to be as secretive as possible at all times.
- The Young Justice series has the Team (and sometimes, their Justice League mentors) use dead drops when they're operating under plausible deniability ops to insert teams or their gear when they can't do things overtly.
- This is an actual method used by spies in the real world.
- For a non-espionage version, Aram Bartholl started a series of USB dead drops as an art project for the public to use.
- Russian intelligence literally turn over stones in their search for spies. The fun part? It's entirely justified.
- The CIA invented a hollow spike that could be pushed into the ground and used as a container for a dead drop. On one occasion a spike was retrieved and brought back to the United States, only to set off a Geiger counter. Turns out the KGB had found it and contaminated the spike with a lethal dose of radiation.