Here we can speculate about the Season 2 mystery as it unfolds and share our ideas.
I am convinced now we know The Powells were once friends with Nicholas and Dahlia that Nicholas was the one who ran over the Powell's son15 years ago. The timeline does add up as in Season 1, the Powell's son would have turned 21 and would have been six when he died.
Just a thought. Can't figure out what Opal has to do with all this though. Thoughts anyone?