Quick Hooks: An Enemy Approaches!

A good, quick hook for a party of any size, experience level, or motivation; as easy to work into an epic saga spanning three MacGuffins and four double-crossings as it is to work into the lowest of low fantasy concerning a ragtag band of dirt theives. The Enemy Approaches works on a variety of levels, as it appeals to the character's love of combat, combined with a guilt-free enemy in many cases, and then there's always the possibility of support from other quarters. 

A couple of examples:

• A small band of foreign slaveraiders make a strike into the night, capturing men and burning buildings. If you can't stop them from getting away with their prizes, can you stop them from getting back to where they came from? Alternately, the players become captured and are now enslaved to cruel masters. Can they win their freedom?
• A small army with the permission of the ruler of the land arrives, and demands taxes. The town is unable to pay them, so the army decides to take what they can instead- sheep, swords, armor, horses, food, personal belongings, etc. Any who resist are put to the sword. Alternately, the town hands over a sizeable chest of gold, and hires the players as reliable mercenaries to guard it until the army can commandeer a sturdy enough cart to wheel it away. During the night, theives attempt to steal the gold. Are they merely run of the mill burglars, are they Robin-Hood style defenders of the people, or are they revolutionaries trying to stir up bad feelings between the king and his people?
• An unknown army approaches. The town guard wants to send the party as scouts to figure out where they're from, what their likely objective is, and whether or not they're hostile. Alternately, they simply arrive and set up camp outside the city walls, apparently setting up a siege without any warning. No passage inside or outside of the city is possible.
• While the players were away, the city has been taken over with minimal resistance. Other than different town guards, most of the helpful citizens are still in place. They speak of the invading army in mostly positive terms, as they made an effort not to slay those citizens who did not resist or fight. The players' money needs to be changed to the new currency, possibly making the players poorer as the moneychangers take their cut. Alternately, the invaders won through hard-fought battle but the new city is subdued. Many buildings are still smouldering or collapsed, and catapult stones litter the streets. The citizens that remain are stubbornly against the new occupants and grudge the players their absences. The undercurrent of resistance is strong, though the new ruler may or may not be just and fair.