So Charlie is obsessed with work after Don's almost died in the hospital.
He designes a cluster theory, which at first is considered only post traumatic stress behavior due to his brother's accident.
But as the killings pilled on, and more facts are thrown into the mix with the help of our geek conspiracy friend (who I forgot the name by the way..), everyone starts to believe it's the real deal.
Aside from the geek guy's weird behaviour, I like how Don was just playing it cool. He's been having that identity and religous crisis since he shot that woman in the car with the sniper rifle. But now he seems focused and calm. Good for him. Hope to seing him in action in the next episode!