Our intrepid adventurers kind of, sort of knew each other. Ramer and his daughter Phayeelor have a reputation for being capable with fighting and magic respectively. Likewise, Shacree is known for her skills with hunting and her family is well-established in Saltmarsh. Bumdug is the odd one out; the gnome has a tendency to blend in, his light fingers liberating pies from windowsills all about town. It was dumb luck that he was in the right place at the right time for a job to present itself.
"Job" is not really the right term for it. "Opportunity" fits better. See, Shacree and Phayeelor are young, a bit bored, and on the lookout for adventure. When they overheard someone in the Wicker Goat talking about a haunted house a short distance to the south of town, it was impossible to pass up. Ramer, though he discouraged going, followed to protect his daughter. Bumdug went because, well, why not?
They made their way to the house through inclement weather. After a brief encounter with some weasels outside, the party made their way to the interior. They immediately went up the stairs and came in conflict with swarms of spiders, which very nearly overwhelmed them. After handling the spider plague, the adventurers found Ned Shakeshaft, bound to a bed. They were in need of rest and wanted to get Ned to safety, so they left the house and headed back towards Saltmarsh.
On the road, the party questioned Ned and suspicion of the man grew. They eventually bound him, figuring out that he was in league with thieves or smugglers. Unfortunately, he managed an escape, but it didn't last long. In attempting to run, Ned plummeted to the water from tall cliffs and did not survive.