1. Death Penalty By Drowning
Characters are captured and accused to be spies or other henchmen of evil out of no reason. The village they are in just finds characters outsiders and vile. They are in the jail of this city and are judged to face death by drowning. There is nothing they can do, no escape, no reasoning to get free as the villagers have set their mind.
The last evening before drowning, an elf slave gives the last meal for characters. In her eyes characters see deep sorrow and fear, as she gives the soup and tea. If any of characters refuse to feast, she insists them to eat, or at least drink the tea (make sure characters do).
Night comes, and characters are forced to nearby lake chained to a heavy rock pulled by mules. They hear their final judgement, how the evil must die and are cast to the lake.
When they cannot anymore hold breath, they realize they can breath underwater (the tea was actually "breath underwater potion"). Guards and villagers think that characters are done and leave the place.
Underwater, chained to rocks characters are alone in the night and now is their change to escape. Give every character a change to get free, or those who got free to help their comrades. Powerful warrior might with successful roll force himself free or rogue might use debris from the bottom to picklock the chain.
When characters swim out of the lake, they get a ghastly vision of this elven slave.
"I am elven princess' cousin, and was captured to be slave.
I freed you, as I saw your soul and you are not evil.
Help me free, as I helped you free yourself."
Now it's up to characters, will they help elven princess' cousin from these narrow minded villagers, who are the true bad guys, or will they just escape the whole place.
How will they plan the freeing? Their equipment are in guards hut in the chest. They might sneak in and kill a couple of guards off-guard or what ever DM seems fit or what ever players find their plan to be.
2. Snakes On The Plane
In big central city, everything has been normal to this day, until in dusk sky turns greenish purple like a vortex and these mighty snake-man warriors attack it. They kill guards and men who resists and plan to make others slaves for their evil reign. Characters might encounter one or two, but they soon realize these vile snake-man monsters are tough opponents, and there are hundreds of them. City cannot defend, nor can characters.
In the disorder city's mage's guild's officer pulls them aside and leads them to secret dungeons below mage's guild. There he tells what is going on.
"From another plane, these snake-men cape to conquer our realm. They are powerful here, as their Plane's laws are more powerful than ours. You heroes are our only hope. You must travel to this Snake Plane and destroy what ever force keeps the vortex open and gives Snake Men power to function on our Plane."
Mage officer then gives magical items for everyone (one item per player) to help their task and opens Plane vortex what leads to this Snake Plane where Snake Men reside.
In Snake Plane player characters are as powerful as these vile creatures and can fight them off. They find it out, as where they are teleported by the vortex there are few guards they can kill easier*. They must travel the palace of Snake Men and destroy the crystal what powers their vortex and allows them to roam free.
* Fix Snake Men stats. At players' realm make their stats insanely powerful, but at their plane downgrade them to meet characters' level.
3. Sickness in Camp
At their travels, characters find a big camp. It's more like a village, but inhabited by nomad tribe. As they go closer to find better shelter than just their tents and campfire, or restock their rations, they soon find out that every single villager is sick and dying. Nomads ask for help.
The sickness is caused by poisoned well's source underground in the mountain or hill. In the source of well the water is green and there is magical crystal what makes the water poisonous. When the crystal is removed, water is restored to healthy.
They find some kind of hint or clue, where the crystal might originate. The clues lead them to nearby village. The leader wants nomad lands for himself, but nomads refused to leave their ancestors place. So the leader decided to poison and kill the villagers to gain their lands.
Will characters help the nomads?
4. Lost Books
There are books lost from mage's guild and one apprentice with them. He was known as power hungry and wanted to learn dark and harmful arts, necromancy in top of it what did not suit guild as he was too young and naive for that kind of power.
Lost books and power hungry apprentice can be found nearby in the mausoleums of cemetery deep underground guarded by undead monsters.
5. Too Big
Thousands of years ago, evil wizard destroyed the mighty dragon and was severely wounded after the battle. With his last powers, he only could cast a sleep spell on the dragons progeny. Now the dragon is awaken, adult. Too weak to do barely anything and stuck overgrown in his cave. Telepathically this dragon asks help from characters to get free.
People remember the tale, but are cautious about dragons. Is this ancient dragon evil or good? Will characters try to free him and how will they get him out of whole mountain?
But the dragon knows where his mother hide the great treasure and is willing to share it with his liberators.