What Kept You?

The audience is all prepared: they've been following Our Heroes back to the villain's lair, and they bust the door down, all ready to put in the big rescue moment...

Only to find that the resident Action Girl/Chick/DistressedDamsel has managed not only to halfway escape, she's done one better and completely wrecked the villain's current operation and might even have the villain tied up with a neat little bow, too.

May sometimes be combined with Pity the Kidnapper; in that case, the "captive" is so obnoxious that the villain ends up begging the heroes to take her off his hands when they arrive for the big damn rescue. Compare Hands Off My Fluffy, where a rescue is also unnecessary.

If a Badass does this, it means they were a Badass in Distress. If a Damsel in Distress, it could mean they are evolving into a Badass Damsel. For a Faux Action Girl, it means they've shown their credentials and become a true Action Girl.

Deconstruction usually occurs if someone barely makes to the destination beforehand. They quickly (with slight panic) adjust themselves and then "calmly" ask this when their audience arrives.

Examples of What Kept You? include:

Comic Books

In Carl Barks' final story Horsing Around With History, Scrooge confidently brings the Trojan Horse into his money bin right before Donald and the boys, back outside, realize the Beagle Boys have been spying on them and must have been hiding inside the Horse. They hurry to warn Uncle Scrooge...only to find him holding the Beagle Boys at cannon-point, having realized something was up because finding the Horse was too easy.

Fanfic

In The Legend of Spyro a New Dawn, Ember gets captured by the Gargoyles and taken to their slave mines. Spyro and Cynder mount a rescue, sending Sparx ahead to warn her. When they arrive, they're greated to the Warden being blasted through a wall. Turns out Ember Took a Level in Badass (getting upgraded from Badass Normal to Badass Abnormal) and had been waiting to get word they were coming and escaped, took on the Warden herself, freed the slaves with Sparx's help, and was just wrapping up her boss fight.
In Tiberium Wars, the GDI forces sent to liberate the White House find themselves a bit late to the party, as the Nod troops around the White House were already cleared out by the (retired) Colonel Nick "Havoc" Parker and his ragtag resistance force.
With Strings Attached has a moment near the climax where the other three are steathily coming to rescue the mind-controlled Paul, only to find him free and happy, having wrapped his captor up in her own robes. Turns out that Paul had shaken off the mind control almost immediately and had spent the last day and a half only pretending to be her slave so he could bugger up the baddies' plans.

Film

In Mongol, Temujin rescues his wife from the Merkits, one of whom had taken her as a wife. When he finds her, she's already murdered her new husband and is ready to go.
Happens in Police Academy 5...sort of. It turns out that the kidnapped policeman thought it was an exercise, so he played along. The moment the would be Big Damn Heroes explained that it wasn't, he immediately KO'ed all his captors.
At the end of Ever After, Prince Henry shows up to save Danielle, but she's already freed herself.
Used in Space Mutiny, and probably the only genuinely amusing part of the original film.
In Hudson Hawk, the title character and Tommy Five-Tone break into a castle to save Anna Baragi. She kills Minerva Mayflower, escapes, and meets up with them.

Hawk: Anna! We're supposed to be saving you.
Anna: I know. I got bored so I saved myself.

Played completely seriously in Shrek: The Final Chapter.

Literature

It's been around since The Ransom Of Red Chief, which makes it Older Than Radio.
Mack Bolan charges into a house full of terrorists, only to find his girlfriend April Rose is holding them all at gunpoint. She quips that it's just like a man to leave the cleaning up to a woman.
Played straight in The Otherworld novel Stolen, but from the captive's point of view. Elena escapes from the compound where she's been held prisoner and stumbles across her lover Clay just outside. Clay had shaken off the drugs, slipped his babysitter, located the compound, and was trying to figure out a way inside when she came out. He is allowed to provide the getaway car, at least.

Live Action TV

The Robin Hood episode of Star Trek: The Next Generation featured just such a subversion. Given the character stuck in the Maid Marian role, Picard really should have seen it coming.
In one episode of Buffy the Vampire Slayer (the one with where the whole town turns into Moral Guardians), the episode ends with Oz and Xander crashing through the ceiling after Buffy has dealt with the Monster of the Week.

Xander: We're...uh...here to rescue you.

Happens so often in NCIS that any time a scene cuts away from one of the team members apparently Alone with the Psycho, the viewer may expect them to have handled the situation by the time the cavalry has arrived. Notable examples from the third season alone include "Under Covers" (Tony, despite being tied to a chair), "Frame-Up" (Abby), and "Bloodbath" (Abby again); it's also happened to McGee and to Ziva at least once each.
In the Smallville episode "Exposed", Lois is knocked unconscious and kidnapped by the bad guys (as she is prone to be) who attempt to escape by helicopter. Clark pulls the helicopter out of the sky and rips open the door only to discover that Lois has come to and is the process of beating the snot out of the bad guys. To add insult, she didn't even notice the helicopter being pulled out of the sky.

Lois: "Hey, 007. Nice of you to show up."
Clark: "I'll start assuming that means thank you."

Happens to Diana in an episode of White Collar.

Tabletop RPG

Traveller. Book 0 (1981) explains roleplaying by describing a fantasy RPG scenario. A princess locked up in a tower lures a guard into her cell, knocks him out and escapes, then meets the heroes who are breaking in to rescue her.

Theater

In the last act of Matthew Lewis' classic Gothic play The Castle Spectre, the heroine Angela's boyfriend and his troops storm the castle to rescue her... and show up after she's stabbed the villain Osmond, saving herself and her father. Granted, Percy did stop Osmond from raping her in Act I, but she took a level in badass between then and now, turning from a traditional Gothic Damsel in Distress into a Badass Damsel. Here's to Lewis, Hidden Depths, and subversion of then-standard gender roles!

Video Games

In The Secret of Monkey Island, Guybrush goes through great trouble to rescue Elaine from LeChuck, finally arriving at the church to interrupt their wedding, with the weapon ready to kill him. But it turns out Elaine had already escaped, and was using a pair of monkeys to disguise in her dress to fool LeChuck, and Guybrush entering just caused the monkeys to flee and screw up Elaine's plan.
In Chrono Trigger, you can escape from the prison or wait. If you escape, you will meet Lucca near the exit, as she has broken in to save you (which she does if you choose to wait).
- If you escape, however, you get some extra items...
In Final Fantasy X, when Tidus, Lulu and Kimahri go to rescue Yuna from the Al-Bhed Psyches, after beating the machina boss Oblitzerator, the hatch on the ship opens... and out walks Yuna, completely unharmed, while a would-be captor slides to the ground. The only comments? Lulu: "I hope you hurt them." Yuna: "A little."
At one point in Dragon Age: Origins, your character is thrown into a prison, and if you choose to escape, you arrive at the prison's exit right at the same time as your companions come busting through to rescue you.
In Final Fantasy XIII, Sazh and Vanille are captured and awaiting public execution aboard a flying battlecruiser. Naturally, the remainder of the party decides to storm it and rescue them. The two prisoners make use of the distraction provided by their allies to escape and meet up with the party roughly halfway.
In Assassin's Creed Brotherhood, at the end of Sequence 5, Ezio returns to the Rosa In Fiore to find that the Templar guards followed the courtesans back after the assassination. He rushes inside, prepared to fight them off and save the day... only to find his sister Claudia standing over the dead Templars, a knife in hand. At Ezio's surprised expression, she shrugs and says "What?" Ezio quite proudly remarks afterward that "My sister knows how to wield a knife."

Web Comics

Order of the Stick has Haley
In Darken, Casper and his partner, Jade, are caught during a break-in in the laboratory of an Evil Overlord wannabe. After breaking out of a truly classic Death Trap, Casper rushes to save Jade...and finds her choking the life out of her guard with her chains. Of course, that's not how he tells the story, but that's another trope.
How I Killed Your Master: Liu Wong previously escaped from another fight with the help of Action Girl Fang Lin; she stayed behind to hold them off. Later, having bumped into one of the friendlier factions in the city and gotten their help, they and Wong are about to rescue her when someone gets punched through the brick wall in front of them. Three guesses who was on the other side.
Taken to an absolute extreme in Adventurers! with Karashi. She is kidnapped twice, and both times manages to free herself. One time she does it so quickly that she makes it back to the party's campsite before they even notice she was gone.

Web Original

Happens in Yu-Gi-Oh the Abridged Series. Our heroes have fought through an entire video game world to rescue Kaiba, only to discover that Kaiba is already free and has defeated who he thought was the Big Bad. Of course it turns out that they're not quite out of the woods yet, but still...

Western Animation

There was a scene like this in Titan A.E., when the Valkyrie's crew come bursting in to rescue Akima from slavers, only to find Akima with a bunch of unconscious slavers lying all around her, wondering what took them so long.
An episode of The Venture Bros features Brock, Orpheus and The Alchemist racing to stop Venture from selling his soul to Henry Killinger; when they bust in, they discover Venture has fired Killinger, and he and his henchmen leave peacefully.
- It's not only this but also a case of Venture stabbing the scorpion; we see Venture signing what we believe to be his contract essentially become a supervillain while Brock and company run through the building. They get there moments too late...only for us to then find out it was Killinger's severance pay for his services.
In a DuckTales (1987) dream sequence, Goldie is kidnapped by the Beagle Boys, and manages to beat most of them and rescue herself. However, when she realizes Scrooge is coming to save her, she up and pretends to still be in danger just for a Rescue Romance. Well...this is Scrooge's fantasy...
In the My Little Pony Friendship Is Magic episode "A Dog And Pony Show", the group comes to rescue Rarity from the Diamond Dogs that kidnapped her. By the time they make it to her, she's already subdued the Diamond Dogs by purposefully being as whiny as possible and was just leaving when they arrive.
In a Danny Phantom episode, Perky Goth Sam Manson gets kidnapped by a ghost who is King of a Medi-evil realm to become his bride. Danny and Tucker rush off to save her...but intervene when she was about 20 seconds from making her escape, and pretty much ruin her plan.
In the G.I. Joe episode "Glamor Girls", several women, mostly models but including Cover Girl, Lady Jaye, Zarana, and Low Light's sister get kidnapped by a vain old woman who wanted to drain their youth to restore her own. The Joes storm the base but find that the girls have already beaten up the mooks and just need a ride home. Duke awkwardly says, "I'm glad you're on our side." The Joes still needed to save Low Light's sister, who was strapped to a chair and directly in the villain's clutches.