The Cataclysm :
Sages and seers warned it would come, but the world didn't care. They thought it wouldn't matter - So what if a rock from space was heading for them? And so, when it finally arrived within their orbit, the worlds highest mage reached out with his magics to bat it aside.. and he was sent flying as the rock reflected his spell back at him. Others tried - Transmuters could not alter it, Evokers could not destroy it, Abjurers could not stop it. And so the Allmighty Warlord atop his Great Prismatic Wyrm went up into the sky. The world watched as the rock grew larger in the sky, and the warlord dwindled from sight.. how big could this thing be, they wondered? The Seers watched the Warlord as he approached the massive Rock, wielding his magical Adamantine blade and attempting to cleave it in two. They nodded sadly as the blade disintegrated, followed closely by the warlord and his dragon.

The rock was stronger than Adamantium, radiated a powerful and strange anti-magic, and killed any who approached it.
With only a few hours left, a young gnome finally came upon the solution - Technology. Nonmagical explosives, and LOTS of them.
The gnomes gathered all they could find, compressing them into a tiny canister and firing it at the rock.
The largest fireball ever seen lit up the sky, hotter and brighter than the sun for the few seconds it flared, and as it died away, the rock was seen blown to bits! The crowds rejoiced, for their world would not be crushed... But the sages again shook their heads sighing, and retreated deep into the earth as the thousands of smaller rocks began to rain down, each causing a great impact and explosion as it hit the ground. The Meteor shower lasted for 3 days during which Empires were destroyed, whole races wiped out, and civilization ceased to exist.

Aftermath:

That was a few months ago. You've been hiding in the remains of The City since. The creatures that were left alive outside seem to have devolved into barbarism and extreme aggression as they struggle to survive.
When the shower ended, there were over two dozen survivors who managed to gather in this city. Since then, you're down to 8.
The city isn't safe, but what else can you do? Rebuild something defensive here, and hope other survivors find you? Or go out and try to find them?

The old man amongst you, a wizard named William who has lost his spellbook, knows of a tower a few days away that may still stand, and could provide you with a stable base to start from... if you can make it there.

You awaken this morning as you have the past few days. You've enough supplies to last a few more days before you'll have to venture out into the city streets to look for more - A dangerous task, as the more feral survivors are out there, just waiting for a chance to kill. It takes nearly an hour before anybody notices that the youngest of you, a 16 year old human girl, is missing.