About a hundred years ago I posted here about patterns in fiction. A quick recap:

A pattern, then, is first a problem defined, and then a potential solution. This order of precedence is important. Patterns begin with an understanding of challenges and requirements. Solutions flow from that basis. It’s not enough to know how to build an archway, for example, you need to know why an archway is right for particular set of conditions in a courtyard.

Patterns are named and collected in catalogs. They tend to work together. A pattern defines a problem, suggests a solution, which creates conditions that might form the problem for other patterns in the same catalog.

So what might a fiction pattern look like? Here’s an attempt to render a pattern I noticed recently. You see it a lot in caper and escape movies. Ancient historians liked this one too.

The Plot is (not) up (actually)

You wish to provide a false climax. Also to demonstrate stakes, to raise and prolong tension as you approach the climax of a plot, escape or caper.
An adversary (not necessarily the antagonist) waylays the plotters and claims she knows exactly what’s going on around here. Convinced they are discovered, the plotters prepare to fight their way to escape or victory. Weapons are cocked, sweat beads at temples, eyes dart. Then, just in time, the adversary announces her secret. It’s a minor transgression, unrelated to the matter at hand. Tension is released, but left higher than before, since now we know how desperate the plotters are, and how precarious their situation.
A plot, escape or caper is the most obvious context for this pattern. The protagonist must have something to hide, with the stakes of discovery high, and a mission which the adversary seems to set to foil. May also be applied to a romantic assignation of some kind.
A fake discovery followed by a moment of despair and threat. Then the real nature of the discovery is revealed. The protagonist continues on his way, shaken but determined.

GUARD: I know what you’re up to you know.
WILKINS: You do?
[The party tense. A knife is drawn surreptitiously. It’s clear they’re going to have to kill him]
GUARD: Oh yes, you are keeping your best players in reserve, Wilkins. It’s not cricket, you know.
WILKINS: You always could see through me, Mr South.

In a variation, the adversary’s news is more than a minor distraction. It is important enough in its own right that it changes the course of the story. In this case the false ‘discovery’ still provides an initial shock. And as before it serves to ratchet tension in that the protagonist’s peril and desperation are both revealed. Additionally, though, the new mission piles on its own stakes. Those for the core plot remain powerful in the background, though, and will likely reassert themselves in a surprise crisis, probably at a key moment in the new mission. The pay off here is that the original thread is transformed into something even more urgent as it reappears, and with an impact enhanced by surprise.

GUARD: Stop!
[The party tense, ready to fight or flee. One of them kicks a rug over the tunnel mouth. WILKINS reaches into his pocket for his knife, approaches the GUARD]
WILKINS: Mr South?
GUARD: It’s Mary. I think she’s… please. You’re a doctor.
[We follow the characters, and the action, to the stricken Mary. Later, with Mary on the verge of death and our emotions invested in her fate. Two guards enter the empty rec room.]
GUARD2: A black bag, he said. With medical instruments in it.
GUARD3: What about over here. There’s stuff here.
[as he looks at the bags of rubble, and the poorly disguised tunnel mouth, his expression changes from confusion, to grim comprehension]
GUARD3: Sound the alarm.

Related patterns:
This is similar to You (didn’t) already know then (after all), a pattern in which a mission to break bad news is disrupted by a recipient who already seems to have got the message.
Known uses**
Julius Ceasar, William Shakespeare:

    I wish your enterprise to-day may thrive.

    What enterprise, Popilius?

    Fare you well.

    Advances to CAESAR

    What said Popilius Lena?

    He wish’d to-day our enterprise might thrive.
    I fear our purpose is discovered.

    Look, how he makes to Caesar; mark him.

    Casca, be sudden, for we fear prevention.
    Brutus, what shall be done? If this be known,
    Cassius or Caesar never shall turn back,
    For I will slay myself.

    Cassius, be constant:
    Popilius Lena speaks not of our purposes;
    For, look, he smiles, and Caesar doth not change.

The Civil Wars – Book II, Appian

Games were going on in Pompey’s theatre, and the Senate was about to assemble in one of the adjoining buildings, as was the custom when the games were taking place. Brutus and Cassius were early at the portico in front of the theatre, very calmly engaging in public business as praetors with those seeking their services. When they heard of the bad omens at Caesar’s house and that the Senate was to be dismissed, they were greatly disconcerted. While they were in this state of mind a certain person took Casca by the hand and said, “You kept the secret from me, although I am your friend, but Brutus has told me all.” Casca was suddenly conscience-stricken and shuddered, but his friend, smiling, continued, “Where shall you get the money to stand for the aedileship?” Then Casca recovered himself. While Brutus and Cassius were conferring and talking together, Popilius Laena, one of the senators, drew them aside and said that he joined them in his prayers for what they had in mind, and he urged them to make haste. They were confounded, but remained silent from terror..