When six conniving high school teachers, who are best friends, go on their annual lakehouse bender, things begin to spin out of control when two inept goons show up inquiring about a missing briefcase.

Much appreciated!

While six devious school teachers celebrate their yearly retreat..."

This is very complex. Your asking the reader to juggle four clauses (with three different subjects) and three adverbal phrases. I'd toss out at least a third of your details. Sure it's all good stuff, but it's a lot to take in. Maybe edit the whole thing down to 1 or 2 important clauses and 1 adverbal phrase?