A MacGuffin is an object, document or goal that drives the plot because the characters want it — while its actual nature stays largely irrelevant to the story being told. It gets people moving, puts them in each other's way, and gives the chase a shape. What it is made of, or does, is almost beside the point.
The term is associated with Alfred Hitchcock, who used it to describe precisely this device in his thrillers: the thing the spies are after, which the audience does not need to understand in order to care.
The test: could you swap this object for a different one, invent a new name, and leave the story essentially intact? If yes, it is a MacGuffin.
How to recognise one
It is wanted by more than one party. A single person wanting something is a goal. Two or more parties wanting the same thing is an engine, because now every scene has a competitor in it.
Its properties are vague. Nobody explains the mechanism, and nobody needs to. Vagueness is a feature: the less specified it is, the more each character can project onto it.
The story is about the pursuit. What you remember afterwards is the betrayals, the journeys, the deals made in bad faith — not the object sitting at the end of them.
It can be replaced. This is the decisive one. If swapping it changes nothing, it was never carrying meaning; it was carrying motion.
Examples, and one that does not qualify
In Casablanca, the letters of transit are a MacGuffin in the purest form. Nobody in the audience is invested in travel paperwork; the letters exist so that two people must decide what they owe each other. In The Maltese Falcon, the statue is almost a joke about the device — and the famous closing line makes that explicit. In Pulp Fiction, the briefcase glows and its contents are never shown, which is the device acknowledging itself.
By contrast, the One Ring in The Lord of the Rings is not a MacGuffin. It corrupts whoever carries it, it tempts individual characters in individually revealing ways, and the plot would not survive swapping it for a crown or a map. When an object produces the story's meaning rather than merely its movement, it has stopped being a MacGuffin and become a symbol — which is a different and usually better thing to build around.
Three devices people confuse with it
A red herring is designed to mislead: it points the reader at the wrong answer. A MacGuffin does not mislead anyone — everybody is openly chasing it. See what is a red herring.
A planted detail that must pay off is the opposite principle: it is introduced quietly and must matter later. A MacGuffin is loud and need never explain itself. The rule it breaks is set out in what is Chekhov's gun.
A device that solves the plot out of nowhere is a failure of causation, not a motivator — what is deus ex machina. A MacGuffin starts trouble; it does not end it.
How to use one well
Make the want specific even if the object is not. You can leave the briefcase unopened. You cannot leave vague why this person needs it. The object is allowed to be thin; the desire is not.
Let it put the characters in rooms together. Its real function is collision. If the pursuit keeps everyone usefully apart, it is doing nothing but adding travel.
Decide early whether you will ever show it. Both choices work; drifting between them does not. A reveal that is neither a surprise nor a refusal is the worst of the three.
Do not let it absorb the ending. The last pages should resolve what people wanted it for. An ending that resolves only the object leaves readers oddly unsatisfied, which is part of what how to write a satisfying ending is about.
Where it goes wrong
Two failures recur. The first is explaining it too much: once you spend a chapter on how the artefact functions, readers reasonably expect that mechanism to matter, and feel cheated when it does not. Mystery costs nothing; detail creates debts.
The second is hoping the object will do the emotional work. A MacGuffin can carry a plot a very long way, but it cannot make anyone care. The caring comes from what the pursuit costs the people doing it — which is why a chase with nothing at stake personally reads as flat no matter how fast it moves, a pacing problem more than a plot one: see how to pace a novel.
Why serials are a good place to test one
A MacGuffin is a promise, and promises are measurable when readers arrive in instalments. If the comments on chapter five are all about the object, your readers are invested in the wrong thing; if they are arguing about who deserves it, the device is doing its job. We make Arwy, an Android app where books are published chapter by chapter and readers comment as they read. It will not tell you whether your plot works — only your readers can — and if you prefer to finish a whole manuscript privately before anyone sees it, a serial platform is the wrong tool for that.
Writing a chase of your own? Readers will tell you if the prize is working. Arwy is on Google Play.