You may know the scene. The hero has half of something, like a letter, a Treasure Map detailing the MacGuffin's location, or a MacGuffin proper; but without the other half it's useless or indecipherable. Eventually they casually mention this to a friend or a rival... who then double-takes and pulls out the other half.
The details of this scenario can vary. Usually both characters wind up with the halves independently, having been aiming towards the same goal the entire time. The discovery of the other half can lead them to either quickly start working together (a convenient excuse for a Rivals Team Up), or start fighting each other for the other half. Another variation has the characters receiving the halves at the same time, but due to the passage of time or other circumstances, they are not aware any more of who has the other half; at least until said owner reveals it.
It doesn't have to be a map, letter, or MacGuffin; it can be any important clue that's divided in pieces and worthless if not whole. It also isn't restricted to just two halves; it can be several pieces in the hands of several characters, making up a "collect the plot coupons" story.
This trope does not refer to an object simply being separated and handed over to different people in full knowledge of who the owners are. There has to be a certain element of surprise, or at least a lack of willingness on who gets each half if the separation is forced.
Closely related is an everyday object - a business card, a dollar bill, a coin, a plastic token, etc - that has been torn/broken in half as a means of identification; as it's extremely unlikely that another broken object will match up with either piece, it can be used as a relatively secure equivalent of a Trust Password.
Related to Dismantled MacGuffin, which can be a good source for these situations.
- Secret of Twilight Gemini's plot centers around the search for both halves of the eponymous diamond. Lupin receives the first half from his old mob boss Dalune, who tasks him with finding the other half. Which is eventually revealed to be held by Lara, Dalune's granddaughter.
- In Kill la Kill, the main character Ryuko Matoi transfers to the main setting, Honnouji Academy, armed with one half of a sword-sized pair of scissors. She is in search of her father's killer, who stole the other half of the blade from him. The other half turns out to be held by Nui Harime, The Dragon of Ragyo Kiryuin, the true Big Bad of the series.
- In Yu-Gi-Oh! GX, Judai receives half a pendant from the Gravekeeper's Chief, and is told the other half was taken by another duelist long ago. Judai finds out this is Asuka's brother Fubuki, the leader of the Shadow Riders. When he defeats Fubuki and claims the other half, he forms an amulet that protects him from the shadow powers of the subsequent Riders.
- The Castle of Cagliostro has two rings, both have been inscribed with "Capran". Princess Clarisse and her uncle, Count Cagliostro, both have one. The rings have been passed down for generations, the "Light" and "Shadow" sides of the family. When held together, the rings combine to form a new inscription, but wearing the rings means that Lupin can't read it. "When light and shadow are joined, face the Goat on high who faces the sun and tells time, and place me in his eyes." The inscription tells Lupin how to use the two rings to reveal the secret of the Castle of Cagliostro.
- In the A Certain Magical Index movie Miracle of Endymion, Shutaura Sequenzia carries a broken bracelet as a Tragic Keepsake from the plane crash that killed her father. She gets shocked when she runs into Arisa Meigo and finds that she carries the other half, even though they have never met before. It turns out Arisa was spawned from Shutaura during the plane crash and took the other half with her. When the two become one again, the bracelet becomes whole.
- In Gunsmith Cats, Bean Bandit is given a half a dollar bill signed by a New York drug distributor when he accepts a high-value run. The majority of the resulting arc involves him being challenged and/or assaulted for it, as whoever shows up at the meet with the half-bill will be able to walk away with several million dollars in drugs.
- So, I Can't Play H!: According to prophecy, the legendary sword "Gram" will appear when Grimwald faces great peril. It was split in two and passed down among Grimwald's top ranking Houses: the Restall Family which guards the female lineage and the Galdrblog Family, which protects the male half. Lisara is the heiress of the Restall House and used her half of the sword to form a provisional contract with Ryosuke; not realizing the other half lay dormant inside his body and, thus, unwittingly reforged the blade.
- In the Disney comic Il tesoro di Sierra Leone Uncle Scrooge comes upon a talkative parrot who knows the location of a treasure. He only manages to learn the name of the state where the treasure is buried before he must leave for a moment, and in the meanwhile Rockerduck comes along and learns from the parrot the name of the town, but not the state. Both reluctantly decide to pool their knowledge and find the treasure together.
- Turnabout Storm: Phoenix and Twilight Sparkle independently discover the two halves to Sonata's letter of resignation, which once together give Phoenix an important lead for his side of the investigation.
- In the remake of The Parent Trap, Annie and Hallie both have half of the same picture and it's the only picture they have of their Disappeared Dad or Missing Mom. This is what makes them realize they are twins, even though they hate each other at this point. This kicks off the main plot, with them trying to get to know their respective missing parents. (In the original film and the book it is based on the girls had different photos of their parents.)
- In Bedknobs and Broomsticks, Professor Brown has one half of the book that mentions the Substitutiary Locomotion spell, which appears to cut off just as it is about to mention the magic words that activate it. A bookseller has the other half, and has been looking for Brown's half, thinking it has the spell. It turns out neither half has it.
- The Good, the Bad and the Ugly: Tuco is just about to kill his old partner Blondie, but then ends up hearing one half of a dying man's testimony about hidden treasure and its location, before getting distracted and Blondie hearing the other half. Tuco learns the name of the graveyard it's in, Blondie learns the name on the grave it's buried in.
- In Star Wars Episode VII: The Force Awakens, Poe Dameron receives the map leading to the now-reclusive Luke Skywalker, but it's eventually discovered that the map is incomplete. Towards the end, the remaining section of the map is found inside the shut-down R2-D2.
- In The Whole Ten Yards, the MacGuffin is a torn dollar bill, the first earned by a dead mobster; it's actually torn in such a way that each half only has half the serial number, which the mobster used to identify a $280 million account.
- In the second Dinotopia book, Arthur Denison finds a strange key with a spiral pattern on the base. He tries it on a door in the World Beneath but it doesn't work, and it's determined that it's only half a key. The other half is in the possession of a woman named Oriana, who enabled Arthur to continue his expedition, and eventually becomes a Love Interest.
- In Bearskin, the youngest daughter of the family agrees to marry Bearskin in exchange for the financial help he gave to their father, and Bearskin gives her half of an engagement ring, and then leaves, keeping the other half for himself. Some time afterward, he returns cleaned up and handsome, and proves his identity by producing the other half of the ring.
- Parodied rather savagely in Monstrous Regiment. The father of Shufti's baby went off to be a soldier in the Borogravian army, and said he was going to break a sixpence in two pieces and give her one so they'd know each other, but either he never got around to it or (more likely) just plain forgot about her. When they meet again, Shufti has developed enough as a character to turn him down for his unfaithfulness... but not before reminding "Johnny" that he still owes her sixpence.
- In Philip K. Dick's Paycheck, one of the random bits of junk the protagonist has in his position after a Laser-Guided Amnesia treatment is half a poker chip - this grants him entry to a gambling den where he can escape his pursuers.
- An episode of Xena: Warrior Princess included the search for a large, hidden treasure with a treasure map that had been ripped into several pieces. The different people looking for the map were forced to work together as they had memorized their portions of the map and then destroyed them.
- Bones: In one episode the Victim of the Week is a man that Cam used to live with. She wants to adopt his now teenage daughter, who was about 10 when Cam left. At the time Cam gave her half of a hugging kitties salt-and-pepper shaker set, keeping the other half and saying that whenever the girl looked at it and thought of Cam, Cam would be looking at hers and thinking of her. In the present day the girl claims not to remember Cam, but when Cam pulls out her half the girl runs upstairs to bring out hers too.
- In Legend of Earthsea each of the protagonists unknowingly hold onto a half of the Amulet of Peace, the MacGuffin necessary to literally close the door on a realm full of unspeakable evil.
- In the pilot of The Invisible Man, Darien Fawkes goes to meet a government agent at a public meeting place, and is given a torn business card so he and his contact can identify each other. Parodied in that he finds an entirely different handler (or possibly just another bewildered asset like himself!) before finding his own contact - it's such a common trick in such circles that there were at least one and perhaps more sets of cards wandering around that same area!
- Call of Cthulhu supplement Terror from the Stars, adventure "The Temple of the Moon". The Player Characters and two independent villains each receive 1/3 of the Tablet of the Moon, a piece of gold jewelry that allows the user to find the location of a treasure on a map. The players must either defeat one or both villains and take their pieces or team up with them.
- Final Fantasy V, each of the two parallel worlds has one half of an ancient book. When the worlds merge, the two halves do likewise.
- In the Devil May Cry series, twins Dante and Vergil own two halves of an amulet that, when brought together, can open a portal to the demon world or unlock the true power of their father's heirloom sword, the Force Edge.
- In Spartan Ops, the secondary campaign of Halo 4, the Librarian gives Dr. Halsey an artifact called the Janus Key, which records the location of every Forerunner relic in the galaxy. The device is activated by connecting the two halves, and in the scuffle after the reveal, Jul 'Mdama gets one half while Spartan Thorne gets the other.
- There are a few in RuneScape:
- The Shield of Arrav quest.
- The crystal key (which can be used to obtain treasure from a chest) is usually dropped in halves.
- Case 1-5 of Ace Attorney has this in the form of the Evidence List/Ema's picture. Phoenix finds one half, Edgeworth has the other.
- In The Angry Video Game Nerd's crossover episode with Pat The NES Punk, AVGN has a golden copy of Nintendo World Championships, obtained from a Nintendo Power magazine prize giveaway, while Pat has a grey copy obtained from a Powerfest event. They both want each other's cartridge, as they would complete that rare game's collection, and compete for it by playing the game on a reproduction cartridge. After finding out that NWC contained content recycled from Super Mario Bros., Rad Racer, and Tetris, AVGN destroyed the cartridges in a fit of rage (In reality, he only destroyed replicas and left the originals unharmed- and both cartridges actually belonged to Pat).
- In the Invader Zim episode "Tak The hideous New girl", when Dib's Sister Gaz found files containing Tak's plan we get this exchange.
Zim: I'm the only one with the technology to decode those files!Dib: And we're the only ones with the files to be decoded!
- The Simpsons episode "The Way We Weren't" has a younger Marge breaking in half a heart-shaped rock from the boy who turned out to be Homer after he apparently skipped out on a date with her. Homer found the other half after Marge had left. The two put the rock back together years later.
- The Rocko's Modern Life episode "I Have No Son" had Ed Bighead and his son Ralph keeping both sides of an old donut related to the event that damaged their relationship.
- In one episode of Jackie Chan Adventures, Jade took a liking to a boy named Seymour, even giving him a half necklace pendant while she wore the other half. Unfortunately, Seymour turned out to be the sky demon Hsi Wu, who was befriending her to regain another half left behind: his own tail, accidentally severed and kept in Uncle's shop.
- Shazzan: Chuck and Nancy each wear half of a magic ring. When the two halves are reunited, it summons the mighty genie Shazzan.
- In the Spongebob Squarepants special "Atlantis Squarepantis", Spongebob and Patrick find half of an amulet and bring it to a museum, where the other half coincidentally resides.
- In Gargoyles, the Phoenix Gate was introduced this way. Goliath had one half, and Demona had the other. The halves are soon reunited, revealing the Gate's power of Time Travel. The end of the episode shows how the Gate was broken in the first place: a younger Demona, inspired by a human wedding, breaks the Gate and offers one half to Goliath as a token of love.