The plot hook was simple. With such a disparate party of adventurers, there was only one thing to tie them together: a desire to go... somewhere. As such, they met unwittingly in a large city to be hired by a travelling wizard as guards on a trip to a far away mountain range: the Spine of the World.
[1] I left no time for making acquaintances. In a condensed travel montage, the adventurers were forced to move at a brutal pace set by the elderly wizard. Was he truly elderly? After leaving the city's outskirts, he seemed to move with way more alacrity than his supposed age allowed. So maybe. Maybe not.
After a couple weeks of grueling travel, the adventurers reached a mountain range - at this point, they were way too tired to care which or where. The wizard did a disappearing act, and so the party was left in the middle of nowhere, with nothing to do.