Must Let Them Get Away

So, The Hero has been on his epic quest for quite a while now. Never tiring, he's been following the Big Bad valiantly, and now he's finally going to catch up to him. Ooh, there's so going to be an epic fight soon... And then the Hero catches up, he and his companions fight the Big Bad, and before long the Big Bad's running for it, and before the Hero can shoot him and finally end this war, The Heart drags him back and tells him that he can't try to fight the Big Bad alone, the Big Bad's got more people on his side, or better weapons, or that the companions aren't strong enough to fight again so soon -- or even worse, the Big Bad's got a hostage he's using to prevent the Hero from pursuing him. Furious, the Hero can only watch as the Big Bad flees...

Another version of the trope is when the Hero has actually caught the Big Bad, who is due to be tried and sentenced. However, there's some kind of loophole in the system, or the Big Bad's got the best legal assistance ever seen, or the Big Bad's status is enough to get him special privileges. The Big Bad's going to walk, or at least get a lesser sentence, and the Hero can only watch.

This trope is often used to enforce a Status Quo in works, to put off the final fight, or to bring back a Big Bad later for the heroes to finally fight.

Related to Conviction By Contradiction, and might be followed by We Will Meet Again. Not to be confused with Forced to Watch, or Watching Troy Burn.

This is an Ending Trope, so expect spoilers to be unmarked.

Anime & Manga

 * In Digimon Adventure, this is what happens when the Digidestined try to keep Myotismon and his henchmen from entering the human world. The reason is that (a) Gatomon was basically knocking around everyone and (b) the door slammed shut in their faces.

Comic Books

 * In the comic Zot!, Zot signed a contract that laid down the terms for his advertising job...aaand forced him to not even touch the Villain Of The Week and his plot to take over the entire planet.

Film
"Officer Lewis: That son of a bitch is getting away with it and we can't even touch him.
 * Robo Cop 2. At the end, the Big Bad who had OCP create a giant robot that killed many police officers and civilians is walking away.

RoboCop: Patience, Lewis. We're only human."


 * Norrington is forced to let Jack Sparrow escape with the fastest ship in the Caribbean fleet in the first Pirates of the Caribbean movie.
 * Is it this trope if the escapees have previously removed any possibility of pursuit/armed response? The officer explicitly states that they can't catch them and Sparrow and Turner have disabled the rudder so the soldiers can't bring their cannons to bear on them.
 * In Law Abiding Citizen / Engineer, Shelton sees Darby walk away... and shake hands with the prosecutor.

Literature

 * In Time To Depart, by Lindsey Davis, Petro, The Lancer, finally catches a criminal and has him sentenced, but the criminal's status as a Roman citizen gets him a lesser sentence, and Petro has to watch him leave.
 * Later, in The Jupiter Myth, Big Bad Florius manages to escape by taking Petro hostage and leaving him in a death trap so that the heroes must spend time rescuing him instead of pursuing Florius.
 * In Bloodhound by Tamora Pierce, Sir Lionel is eventually caught, but due to his status as a noble and his family connections, he gets restricted to his family holdings, rather than placed in jail.
 * Another Tamora Pierce example: Joren isn't a "big bad" per se, just a minor annoying antagonist for the most part, but in Squire, Joren only gets fined for kidnapping Lalasa, Keladry's maid, due to their respective class statuses as a noble and a servant. In fact this is why he kidnapped Lalasa rather than Kel herself, which would have led to far more serious consequences.
 * of course, the Chamber of the Ordeal doesn't ask for a fine...heh.
 * This happens twice in two separate Judge Dee novels (The Haunted Monastery and The Chinese Bell Murders) and in both cases, the villain/s connections would get them freed were they to go on trial, had it not been for a lucky coincidence (in the former, a bear, and in the latter, a furious mob.)
 * The presence of the bear was a coincidence. What Dee did with it averts the trope entirely.
 * The mob was no coincidence. Neither was the unfortunate absence of troops to control them.

Live Action TV

 * In Life, Crews and Reese arrest a murderer but have no proof. They end up putting him away for the only charge they could get him convicted for- parole violation, which was a mere one year of jail. However, the victim's father was in the same prison...
 * In the same season, when they finally catch Russian mob boss Roman Nevikov, they're forced to let him go when an FBI agent comes in, claims he's an important confidential informant for the feds, and waltzes him straight out the door.

Video Games

 * Played with in the final case of Ace Attorney Investigations.
 * Mass Effect 2: Shows up in Zaeed's loyalty mission. For a bit of background: You're helping him with an outstanding contract to liberate a refinery that's been taken over by the Blue Suns mercenary company. During the course of the mission, Zaeed reveals he has an ulterior motive for taking on the contract: he wants a chance to kill his traitorous ex-partner, Vido Santiago. Shortly afterwards, you confront Vido, and Zaeed deliberately ignites the refinery's fuel lines and sets the entire place on fire, with the enslaved workers still trapped inside, at which point you're forced to choose between immediately pursuing Vido or stopping to help the workers. If you choose the latter, you save most of them, but you catch up with Vido just in time to watch his ship take off. Zaeed is not happy in that case ("You just cost me twenty years of my life!"), but it is possible for a sufficiently fast talker to give him a well deserved chewing out and secure his loyalty anyway.
 * Or just leave him to burn. (He's trapped under a girder that fell on him because of an explosion he caused)
 * Also happens in the "Bring Down The Sky" DLC for the first game. If you want to save the hostages, you have to let the terrorist go.

Western Animation
"Dorno: There goes Neron! He's escaping!
 * Happens often in Samurai Jack where Jack is almost about to defeat Aku, who then gets away.
 * The Herculoids. In "The Gladiators of Kyanite", the Emperor Neron forces the Herculoids to fight in his gladiatorial games. At the end:

Zandor: It doesn't matter, Dorno. As long as he's gone, the threat of these deadly games is ended forever."

"Big Daddy jumps out the window, and swims for it. Slowly.
 * Parodied in The Simpsons spinoff "Wiggum, P.I.:"

Skinner: He's gradually getting away, Chief.

Wiggum: Ah, let him go. I have the feeling we'll meet again, each and every week. Always in more sexy and exciting ways."