Due to the very nature of The Masquerade, one of the toughest things about it is finding other people who are also in on the Masquerade. This is justified since it wouldn't be very good form to go around asking everyone you meet if they know that there's a secret society of aliens or magical creatures living among normal people. If everyone does their job right, everyone in on the masquerade should appear like ordinary Muggles ... even to each other. This trope can lead to some really magnificent misunderstandings, especially in romance situations, and the most obvious sign is when you find yourself thinking "Now if they'd just been honest with each other, we could have avoided a lot of trouble here."
Of course, this type of situation could lead to many surprises. Suppose you're a mystical creature living in a world where mystical creatures are thought not to exist, and you must maintain the persona of being an ordinary person. You know that there are others like you that exist, but other than your close friends and family, you don't know who or where they are. You try your best to maintain your disguise, lying to all the muggles at school and at your job. But one of them is getting incredibly close to your secret. You've known this person for years, and never thought him to be anything more than an ordinary muggle. But when he discovers your secret, it's actually okay, because he has the same secret himself!
In Fantasy Kitchen Sink situations (or crossover) they might have a completely different secret. If not a directly opposed faction, it's usually not a problem, as it is easy to agree to "not reveal your secret if you don't reveal mine."
Of course, it could work the other way around too. The trope is invoked whenever a character maintaining the masquerade discovers that another person, whom they've thought of for a while as an ordinary muggle, is revealed to them to also be a part of the Masquerade. Whether the second person has already known of the first person's involvement in the masquerade is irrelevant.
- In Durarara!!, a great deal of the conflict in the latter bit of the series is the various factions of Ikebukuro butting heads (sometimes very very violently) and maintaining secrets from each other and the public. As such, many, many, many characters that interact with each other don't know that these people are actually part of the Dollars, or Saika's army, or Nebula, or the Yellow Scarves, or the yakuza, or...
- In Mahou Sensei Negima!, Negi and some of his students find out that each other knows about The Masquerade.
- In My Monster Secret, Nagisa (alien) and Shiho (wolf-man) are neighbours and friends, but neither of them knows the other's real nature, despite Asahi and Youko knowing both of their secrets. They finally find out about each other in chapter 126.
- In Sekirei, both Minato Sahashi and his sister Yukari are Ashikabi in the Sekirei Plan. Since one of the major rules of the Sekirei Plan is "You do not talk about the Sekirei Plan", neither of them knows that the other is involved. It gets particularly frustrating because Yukari's Sekirei is an older brother to one of Minato's, and is devoted to finding her.
- Additionally, when Minato and Musubi first move into Izumo Inn early in the series, Minato worries about having to keep the Sekirei Plan secret from their new housemates. It turned out that they're all Sekireis.
- There's a Golden Age DC Comics story about the first meeting between Clark Kent and Bruce Wayne - neither of whom have any idea the other one is also a superhero. (They find out before the end of the story, when they both see the other changing into costume.)
- In DC Vs Marvel, Clark is working with the Planet's new photographer, Peter Parker, leading to a scene where they both try to make excuses to the other in order to change.
- Cassidy meeting another vampire in Preacher.
- The Disney Mouse and Duck Comics have some fun with this in their superhero stories, as the various heroes all know each other in their civilian identities but most secret identities are unknownnote , leading to multiple shenaningans-especially because Paperinik (AKA Donald) is prone to wipe the knowledge of his identity from the memories of anyone who stumbles on it. Most notable (and funny) is when the authors remember that Daisy has one, as in those stories her and Donald hate but grudgingly respect each other's alter ego-and are also attracted to each other, much to their mutual horror (sometimes it's hinted that they've actually guessed each other's identity multiple times, only to forget through sheer denial).
- In Tim Burton's film Batman Returns, Bruce Wayne is dating Selina Kyle; he doesn't know she is Catwoman, and she doesn't know he is Batman. In the book of the movie, Selina even wishes that she'd met Bruce Wayne before she'd become Catwoman. They accidentally reveal their identities to each other when they repeat a bit of flirty banter from their costumed personas while in their civilian identities. They both realize simultaneously who the other person is and that they've blown their own cover as well.
- Mr. & Mrs. Smith (2005), the movie where husband and wife discovered each other's secrets: They were both assassins for hire, working for rival organizations. They find this out when they both get hired for the same job on opposite sides. The whole job is arranged by both rival groups to dispose of the problem their unwitting marriage caused.
- The Man Who Was Thursday: The protagonist is recruited as a secret agent so secret that none of the agents know who any of the other agents are. There are several moments later in the book where he discovers that some person he was suspicious of is actually one of his colleagues (and was, equally unknowing, just as suspicious of him).
- Louis' first introduction to Armand in Interview with the Vampire.
- Fairly common occurrence in the Deryni works set after the beginning of the persecutions, since many Deryni went into hiding one way or another to save their lives. A notable example occurs in The King's Justice, when Bishop Arilan finds Jehana guilt-stricken after she warned Nigel of an assassination plot, knowledge she acquired thanks to her powers. First he tries to teach her through a couple of parables that she had an affirmative duty to reveal what she had learned, and when she retorts that he doesn't understand, he displays his Deryni aura to show her that he actually does.
- Harry Potter: Despite having known about wizards and himself being a wizard for years, he was still surprised to find that Mrs. Figg, one of his Privet Drive neighbors that he's known his entire life, has been in on the Masquerade the whole time and has also been tasked by Dumbledore to keep him safe.
- L.J. Smith's Night World series had a book called "Secret Vampire" that centered around vampire James Rasmussen and his mortal girlfriend Poppy. Poppy is terminally ill, so James reveals himself to her as a vampire and turns her in order to save her life. James has broken the second of two major laws in the Night World: Never tell a mortal about the Night World. (The first is "Never fall in love with a mortal" and he'd already broken that one.) At the end of the book, however, it turns out that, unbeknownst to both him and Poppy, she was really descended from witches and therefore was a member of the Night World, not a mortal.
- The Wheel of Time:
- This is standard procedure for the Black Ajah, an Ancient Conspiracy within the Aes Sedai who serve the Dark One. In order to prevent any Black Sister from having the knowledge needed to betray the entire organization, all Black Sisters except the top few are normally only ever given the identity of three other members. Most members do not even know who the next person up the chain of command is, much less who is at the head.
- When Osan'gar, one of the Dark One's foremost Forsaken servants, infiltrates The Chosen One Rand's forces, nobody outside the Forsaken is in the know — not even the Black Ajah sisters also infiltrating the group. Consequently, when he finally has an opportunity to assassinate Rand, he's promptly killed by a Black sister who thinks she's offing one of Rand's loyal bodyguards.
- In the novel Twelve, vampires have to hide themselves from human society. The protagonist discovers that the "mercenaries" his friend hired are in fact vampires. Later, he is shocked to find out one of the vampires isn't. So the villain could move about in the daylight ... Oh, Crap!. Furthermore, said character had fooled the other vampires into thinking he's one of them. It helped that the vampires weren't particularly strong.
- In The Secrets of the Immortal Nicholas Flamel, Josh and Sophie understandably try to cover up what's going on (the short version is that they're helping Nicholas Flamel stop people from bringing about the end of the world) from their parents and aunt, who they think are ordinary people, and who they fear will Go Mad from the Revelation. The fifth book reveals first that their aunt is a powerful immortal called She Who Watches, then that their parents are none other than Isis and Osiris.
- In the third season, Batman and Robin did not know that Batgirl was Barbara Gordon any more than she knew who they were; Batgirl simply tended to show up whenever there was a crisis. Alfred learned her identity in one episode, however, but agreed to keep it secret.)
- There was also a pair of cross-over episodes with The Green Hornet series. Bruce Wayne and Britt Reid originally met and socialized (they are both millionaire playboys, after all), with neither aware of the other's identity as a masked crimefighter. The villain of the episode - or rather, his Perky Female Minion - actually figures out that the two billionaires are also the two heroes but mixes up the secret identities (thinking Wayne is Green Hornet and Reid is Batman). When Batman proves this wrong, the idea is completely dismissed and the truth never occurs to anyone, including the heroes.
- One episode of Amazing Stories featured the tale of a high-school-age boy whose parents revealed to him that a) they were actually alien scientists who came to Earth to study the "primitive culture" and b) their mission was over so they were returning home. The boy regretfully says goodbye to his High School sweetheart, lying to her about his dad getting a new job in a new city and them all moving away. On the spaceship, just before launch, he finds his girlfriend. Turns out her parents were also alien scientists, and that they are all going home.
- In Forever Knight, Nick's partner Tracy knows that vampires exist and knows that Vachon is a vampire. However, Vachon and Nick hide the fact that Nick is a vampire from her, and she doesn't find out until the last episode.
- Star Trek: Enterprise has a brief example of this in one episode where the crew are disguised as locals while exploring a low-tech humanoid civilization on an inhabited world they've recently discovered, only to find out that the Malurians (another humanoid space-faring species) have already set up an underground base there and have an agent of their own living and working among the aliens disguised as a shopkeeper. When they go to confront him about this, they pull out a tricorder and inform him that their readings show he's not native to this planet. Pulling out some kind of scanner of his own, he takes a brief look at it and then replies "Neither are you."
- Buffy the Vampire Slayer
- In season 4, the Initiative are vaguely aware of the Slayer as a myth, but have no idea she a) really exists and b) is Buffy, while Buffy has no idea that her new boyfriend and one of her college professors are part of a military operation to do what destiny has decided is supposed to be her job.
- In season 7, Buffy has no idea that Principal Wood already knows who she is, or even that Wood knows of the existence of vampires. In turn, Wood is left unaware that the vampire in the basement of the high school is the same one who killed his mother.
- Wizards of Waverly Place: There have been several characters the Russos have met and have known to be muggles to them for quite a while before it was discovered that they were wizards or magical creatures as well. Notable examples are Stevie, Mason, and TJ.
- Common occurrence in New World of Darkness campaigns, due in part to the sheer number of masquerades that know next to nothing about each other.
- Varies. When you're a vampire, werewolf, mage or changeling, you can expect to be inducted to your respective secret society, in which, generally, everyone knows who is who. Thus it's a rare occurence that a vampire is in town without the other vampires knowing (and this is the way things should be— masquerade breach is deadly for the vampires as a whole).
- Meanwhile, the same luxury can't always be afforded by hunters, the Frankenstein monsters, and sin-eaters. Sometimes you don't even know that there are other hunters in your area. And one doesn't need another sin-eater to become a sin-eater, so it's likely that a sin-eater might go a long way without meeting the others.
- Scion has a similar problem by the simple expedient of every scion looking like a vanilla human until they reach godhood (or buy Epic Appearance). While a knack exists to detect your fellow godlings (and gods), there are few means to similarly detect Titanspawn or other creatures of Legend so this can crop up fairly often in play.
- In El Goonish Shive, quoth one high-ranked member of The Men in Black, "the accessibility of magic has always been the real secret". So there's a lot of magic users who have no clue about each other and lose time in otherwise trivial cases. Such as when a wizard's apprentice Noah was trying for days to investigate a magical incident, and since he couldn't tell what it's about and had zero diplomatic skills, he was forced to go the roundabout way through Elliot without telling him anything. Elliot himself being a full-fledged magic-user and knowing about the wizard but not Noah and working with another investigator connected to The Men in Black. By the time he got to his witness (yet another magic user who by this time had a good idea what's going on, but wasn't going to tell Noah anyway), the delay allowed the follow-up incident, which loudly finished off already damaged Masquerade.
- Brawl in the Family has two Dittos posing as humans to each other.
- The Fairly Oddparents: Timmy Turner has been classmates with a rich kid named Remy. After a series of suspicious events, Timmy has decided to spy on Remy and discovered that he also had a fairy godparent. When Timmy asked his godparents why he was never told, the fairies replied that it was against Da Rules for fairies to tell their godchildren about other children with fairies. They have to figure it out on their own.
- The Batman: As in Returns, Bruce and Selina are attracted to each other in and out of costume. Unlike Returns neither ever finds out the other.
- The original Batman: The Animated Series had some of this going as well, as Bruce Wayne took a while to discover Selina Kyle's secret identity (while she never discovered his), while Dick Grayson (Robin and later Nightwing) and Barbara Gordon (Batgirl) also dated in college for quite some time before they figured out each other's secrets.
- Zorro Generation Z: Diego and Maria have no idea of their counterparts being Zorro and the Scarlet Whip, until the last episode.
- Miraculous Ladybug:
- The two main characters Marinette and Adrien have no idea that the other is their superhero partner. This causes some complications in their romantic lives: Marinette loves Adrien, who thinks she's a good friend and has no idea how she feels. Cat Noir loves Ladybug, but she's endlessly annoyed by his constant flirting. The whole mess could easily be solved if they unmasked in front of each other.
- And on top of that, the two are constantly battling the minions of the evil Hawk Moth... who is in fact Adrien's father.