... Or at least they're likely to be mistaken for them whenever the era they travel to is familiar with the concept.
Think about it. If you're from a different time, then you:
- Possess a bunch of knowledge that most people wouldn't have, some of which may very well be classified in the time you've arrived in.
- Lack a bunch of knowledge about pop culture and current events that most people would have.
- Probably have an accent that sounds slightly off.
- Can't convincingly account for your past, because you literally don't have one in that timeline.
- Have goals which probably look incomprehensible to other people, and therefore are likely to be taken as cover for something more sinister.
All of these will make you appear to be a spy to anyone who takes enough of an interest in you to notice.
Compare Fish out of Temporal Water, the root cause of this trope.
- In an Archie Comics story, Jughead accidentally travels back in time to The American Civil War and is mistaken for a Confederate spy (one of the suggestions being that the S on his shirt stands for "Spy" or "South").
- Mortimer experiences this twice in the Blake and Mortimer album The Time Trap, the first when he automatically says he's English... in medieval France. In the second, he's flung into the dystopian future and is found by rebels.
- This happens to Jimmy Olsen in a Silver Age story when he gets transported back to World War II and has to pose as a Nazi.
- The EC Comics story "...For Us the Living" (Weird Fantasy #20) begins with an atomic scientist being arrested as a spy for a foreign power. The scientist admits his identifying documents are all forged because he came from an alternate time-branch in which Abraham Lincoln escaped assassination and brought peace to the world.
- In Hot Tub Time Machine, Blaine and the ski patrol mistake the main characters for Soviet spies after finding their cell phones and MP3 players (which they think are spy gadgets), and their can of Chernobyl energy drink with its Cyrillic lettering (which they think is a bomb).
- In Safety Not Guaranteed, this is happened for different reason: Kennetch is chased because he breaks into nuclear facilities, for the purpose of getting something for his time machine.
- Chekov and Uhura in Star Trek IV: The Voyage Home, in the famous "Noo-klee-ar wessels" sequence. Somehow they don't realize that, if you want to get aboard an aircraft carrier in 1986, the guy with the prominent Russian accent probably shouldn't be your spokesperson. This doesn't cause them any problems in the end except for a bunch of strange looks, but when the inevitable transporter malfunction strands Chekov next to the reactor of aforementioned nuclear wessel he is assumed to be a Russian spy. His recitation of Name, (Starfleet) Rank, and Number do nothing to dispel this. One of his interrogators does express some doubts, noting that while Chekov obviously is a Russkie, he's also "a retard or something" because of Chekov's farfetched claims and Literal Mindedness.
- Played with in The Film of the Book Timeline, where a group of 1999 History students travel to The Hundred Years War France and are captured by English soldiers. A Blood Knight singles out the only French student, who the rest insist is their interpreter in order to protect him (the group is posing as English pilgrims). Claiming that he is going to test if this is true, the knight orders the student to translate aloud a series of sentences that the knight says in French, into English; if the student refuses, the knight warns, he will be proven to be a spy and executed immediately. The last sentence the knight says is I am a spy. When the student painfully complies, the other English soldiers take it as a valid confession and kill him. This is then subverted when it is discovered that the knight is a time traveler himself and he knew from the beginning who the "pilgrims" were. It doesn't help that one of them is Scottish (played by Gerard Butler), and England was at the time also at war with the Scots. The Big Bad assumes that the Scots must be trying to ally with the French.
- Pops up a few times in Time Machine Series gamebook series, such as being taken for a Mexican spy during the Mexican-American war.
- A very common plot in modern Russian alternate history fiction is "modern guy falls into WWII". The first thing that happens to the protagonist is always captured by the NKVD because of this trope, or an attempt of such. How the protagonist convinces State Sec that he means no harm (or dodges them altogether) is the first plot twist in such stories.
- A frequent plot device in Harry Turtledove's Crosstime Traffic young-adult series. While not exactly time travel, the protagonists travel to alternate universes where historical events have departed from their own Future History. In most of the stories so far, they get mistaken for spies. For example:
- In The Disunited States of America the protagonist is travelling with forged identity documents in a war zone and steals a uniform in order to infiltrate a military unit — any of which would get him executed for espionage had he been caught, even though that wasn't his intent.
- In Curious Notions the protagonists are suspected of being double agents by both the Imperial German occupation government and the Triads in San Francisco due to the actions of their predecessors (selling slightly more advanced technology from the home timeline to the locals — against company rules precisely because it attracts undue attention from the authorities).
- In The Gladiator the Crosstime Traffic organization is actually participating in espionage, attempting to subvert the victorious Communist government by reintroducing capitalist concepts to the population in a timeline where the USSR won the Cold War.
- In Johnny and the Bomb, both Bigmac and Wobbler are mistaken for spies when the main characters travel back in time to the Second World War. As in some other examples, the WWII people regard their modern technology as spy gadgets, especially a pocket radio. It doesn't help that the radio says "Made in Japan", or that Bigmac is wearing a German uniform.
- In the third novel of the The Milkweed Triptych, Raybould Marsh barely escapes the End of the World as We Know It by traveling back in time to World War II. Just before he time-jumps, his friend hurriedly gives him his billfold so he'll have some ready cash. Unfortunately the money and identity cards are all from 1963, so he's quickly detained by the police on suspicion of being a German spy with badly-forged documents. This turns out to be an advantage through, as the authorities release him the next day in a Trick-and-Follow Ploy. As Marsh is an intelligence agent, but a British one, he's able to escape their surveillance.
- In Outlander, this is a huge problem for protagonist Claire in the first and second books, especially as she arrives in Scotland during the Jacobite period.
- The end of Robert A. Heinlein's Time Enough for Love involves the protagonist travelling back to the time of his own childhood and dealing with the difficulties thereby. Despite being a 2000+ year old pansexual incestuous time traveler speaking what, after 2000+ years, might as well be a foreign language in a very alien culture, he encounters no problems. However, his plan to escape having to fight in WWI is to hustle pool and flee to Brazil. He then realizes that that might get him killed by German or French agents as a spy.
- Played straight in the novel Timeline. An English knight suspects a shy "Irish" squire (in reality an American student from 1999) of being a French spy and challenges him to a joust to prove that he is not.note
- The Time Scout series doesn't say you'll be caught as a spy, but the results are the same. Get caught, get killed. Usually for apostasy or some such.
- Played for Laughs in an episode of Boy Meets World, in which an accident involving a microwave oven sends Cory back in time to a warped version of The '50s. (It's All Just a Dream.) Notably, they don't get suspicious for any of the reasons listed above, but because he doesn't buy into McCarthyist paranoia and isn't deathly afraid of a Soviet invasion like everyone else in town. He also has knowledge he shouldn't have, such as exactly what Sputnik is (i.e. a harmless metal ball with legs instead of a Kill Sat).
- In Buck Rogers in the 25th Century Buck is effectively a time traveler, having awakened after 504 years into a future he doesn't yet understand. Matters aren't helped by the fact that he is awakened by the Draconians, Earth's enemies, who install a tracking device on Buck's space shuttle to learn how to get through Earth's defenses. Buck is subsequently accused by Earth of being a Draconian spy, setting up the Clear My Name plot that dominates the second half of the pilot movie. Most of the episodes in the first season have Buck utilized as a spy by the Earth Defense Directorate precisely because he's not on the grid. Buck's frequently able to use his 20th century skills to throw 25th century opponents off guard.
- Doctor Who: The Doctor and his companions sometimes fall prey to this.
- Such as when they go to Skaro in "Genesis of the Daleks", where they are mistaken for the Kaleds' deadly enemy the Thals (or their common enemies, the wild mutants that run around in the nuclear wasteland). Everyone being Human Aliens in this case did not help.
- Sometimes the Doctor genuinely is a spy, working for himself, simply by virtue of being too nosy for the villain-of-the-week. Other times, such as in "The Brain of Morbius", the irate locals correctly identify him as a Time Lord but automatically assume he's there to steal their stuff because they're suspicious of Time Lords in general. The eponymous Morbius similarly assumes the Doctor is there on behalf of the Time Lords to hunt him down and was just stumbling into the creepy castle as a ruse. Ironically, it's suggested the Time Lords did dump the TARDIS there (without consulting the Doctor) and just trusted that the Doctor would sort everything out in his usual manner.
- In "Cold War", the Doctor and Clara end up on a Soviet nuclear sub. Naturally, the crew assumes they're Western spies, despite the TARDIS turning their speech into flawless Russian. This leads to an exchange where Clara says she doesn't even speak Russian ... in Russian.
- In the Eureka episode "Founder's Day", a bunch of characters from the present day appear at an army camp in 1947; the general in charge of the camp spends most of the episode chasing them around assuming they're spies.
- This happens to Gary in an early episode of Goodnight Sweetheart. Knowing Himmler and Goebbels' hair colour is what did it; his claims to have seen it in a newsreel fall a bit flat because newsreels were monochrome. He decides to play it up and manages to convince his captors he is a spy, but a British one and not a German one as they'd assumed.
- This is the premise of the K9 episode "The Cambridge Spy": a lightning strike sends Jorjie back to Cambridge in 1963, she's arrested as a Russian spy, and K9 and Starkey have to travel back to rescue her.
- Stargate SG-1: In "1969", the team finds themselves at the bottom of a missile silo in 1969, leading naturally to this assumption. It doesn't help that the interrogator asks them, in Russian, "Are you Russian spies?" and Daniel replies without thinking, "Nyet." O'Neill is not happy.
- Star Trek: The Original Series:
- "Tomorrow Is Yesterday". When the Enterprise accidentally travels back in time to Earth in 1969, Captain Kirk is considered a spy when he's caught infiltrating a U.S. Air Force base. (When an interrogator threatens to lock him up for two hundred years, Kirk ruefully acknowledges, "That ought to be just about right.")
- "Assignment: Earth". When the Enterprise is deliberately sent back in time to Earth in 1968, Kirk and Spock are arrested as spies when they're caught inside McKinley Rocket Base.
- Supernatural. Justified in "Time After Time" given that it's World War Two, and Dean is carrying a fake ID (an FBI badge 68 years out of date) and an electronic device (a mobile phone) displaying the words NO SIGNAL.
Cop: You some kind of jerry spy?
Dean: Jerry who?
Cop: And a terrible one at that.
- In the Netflix series Travelers it is in fact the case that all of the Travelers are spies. A rogue member tries to sell the US government information about how they've been infiltrated by this conspiracy but forgot just how deeply that infiltration went.
- Voyagers!: In "Sneak Attack", Jackie Knox mistakes Bogg and Jeffrey for Axis spies in Pearl Harbor on December 6, 1941.
- In the GURPS Infinite Worlds setting, this trope is played with due to the fact that Infinity Patrol agents routinely do become spies in the Alternate timelines they infiltrate, both to avoid the notice of the locals, as well as to hide from agents of rival Crossworld travelers from the Centrum timeline.
- In Back to the Future: The Game, Edna Strickland is convinced that Marty is a spy named Yako Smirnoff (partially because a different time traveller told her this.) Additionally, Arthur McFly is convinced that Marty is an FBI agent.
- In Chrono Trigger, Crono and his companions are identified as spies by a mysterious prophet who recently turned up in the Kingdom of Zeal in 12,000 B.C. and predicted various events, including their arrival. The prophet himself turns out to be a time-traveling Magus, inverting the trope. That and it can be presumed that he avoids many of the mishaps of being thought as a spy despite his time-traveler status because he actually existed in that past time period and place(as a child) and thus knows the cultural details that the natives there would know.