Colliding Criminal Conspiracies

You know the saying "There's Always a Bigger Fish"? Well, it also applies to crime and criminals. When a story opens with a thief, kidnapper, or murderer "getting away with it" or proceeding with stage 3 of their 4 step plan, they may run into Colliding Criminal Conspiracies when they get entangled along with or caught in the traps of another, bigger or more professional criminal... or monster.

If they took some Innocent Bystanders for hostages, then both kidnapped and kidnappers are going to have to work together if they want to get out alive. Usually though this threat is so grave they fast forward past Stockholm Syndrome and develop true loyalty for each other that can last a lifetime. If they survive, that is.

This isn't to say all is forgiven and the criminals turn over a new leaf, and make them truly sympathetic by pitting them against a truly worse adversary. Quite the contrary, they might show that they're really rotten by showing that after their need for Teeth-Clenched Teamwork has passed, they plan to kill their former kidnap victims, and/or by using the hostages as Meat Shields and dying thanks to their stupidity. Good riddance to that Asshole Victim. Interestingly, both of the above can exist in the same story if one criminal repents and the other doesn't.

Likely candidates for conspiracies to collide into are: Arriving at the home of Mad Scientist, Cannibal Tribe, or some sort of monster. One especially deliciously ironic variant is to kidnap a monster. Due to the high stakes, expect the protagonists (both kidnapped and kidnappers) to have to choose between leaving the loot and living, or getting the gold and potentially dying.

Examples of Colliding Criminal Conspiracies include:

Comic Books

This is the big reveal in Bookhunter. Two different thieves, acting completely independently, plot to steal a valuable book. The first thief leaves a replica in the original's place, and the second thief steals the replica. It's only after solving the mystery of the second theft that the police realize that the first theft happened at all.

Film

From Dusk till Dawn—two gunmen brothers kidnap a preacher and his children, only to take refuge in a brothel/strip joint infested with vampires.
In House on Haunted Hill (the remake) the host and his wife are planning their own roundabout ways to kill each other during the party. Shame it should just happen that the house really is haunted, and filled with exceedingly sadistic and powerful ghosts.
The French movie The Nest has a great example of this. A big warehouse complex is being used as a hideout by some fairly mundane thieves, but ends up as the site for a huge battle between terrorists and a good-guy military squad.
Psycho—A secretary runs off with several thousand dollars and holes up in the Bates Motel. Things end poorly for her.
Splinter—A married couple are taken hostage by a couple of criminals. During a pit stop for gas, they're attacked by a horrible monster that takes over people as it devours them.
In Whisper, a band of kidnapper discover the child they've abducted is very, very much not a normal little boy.
In The Usual Suspects, a bunch of would-be robbers end up stealing from and in the pockets of a much more sinister crime lord.
The plot of Snatch is driven by a variety of criminals vying over a diamond, intersecting with Irish Travelers clashing with an underground boxing promoter.
Lock, Stock and Two Smoking Barrels is the intersection of four lowlifes trying to pay off a gambling debt, a group of thugs stealing from a black gang's pot growing operation, and a crimelord ordering the theft of some valuable muskets.
Worst case yet must be Deep Rising, where a Gambit Pileup has a thief, mercenaries, a captured cruise ship and a pack of sea monsters.

Literature

In Kim Newman's No Gold In The Grey Mountains, a band of thieves try to rob a coach of its gold. It doesn't have any (a Title Drop is deployed), so they opt for a hostage ploy on the little girl who's aboard instead. Back at their hideout, some ancient thing is stirred up, and begins picking them off one-by-one...

Live Action TV

Happens a couple times with rival spy agencies on Alias. Most notable in the early seasons with Sark and his "flexible loyalties." Most of his plans started with big successes, only for him to get caught or entwined in another spy's scheme. He'd then switch sides or at least pretend to, evoking a very temporary truce. Even the finale showed that his tendency to let whoever's conspiracy he collided with take precedence allowed him to be the only Big Bad to survive.

Manga and Anime

Baccano! combines this with the odd case of Mugging the Monster, with everything from trainfulls of rival mobsters encountering a conductor who's an Ax Crazy assassin with a twisted sense of justice (and a great deal of respect for the collegue they murdered to infiltrate the train) to immortals having their elixir of life stolen by random muggers.

Web Original

In The Gamers Alliance, the Nightstalkers end up entangled in the complex rival plots of Matheson Crime Family, the Order of the Black Rose and the Totenkopf cult, all of which take place in Maar Sul City. The gang tries to make the most out of it in the dangerous environment but does suffer quite a bit along the way because they simply aren't powerful enough to upstage the other influential factions in their own game.
Mega 64 Version 3: The antagonistic organization Falz is afraid of a group of incredibly dangerous assassins they call The Killers. It shortly turns out that the Mega64 gang has had run-ins with members of The Killers before.

Real Life

This real life story. Terrorists in Kashmir find a cave to use as a hideout. Cave turns out to be home to a large, pissed-off bear. Hilarity (and two dead terrorists) ensues.
- Only if bears are a criminal conspiracy. Which they are.