Season Four begins six months after Andy and Nick leave for their undercover operation. We return to 15 Division with them - and quickly realize that everything seems to have changed. Adapting to new situations, rolling with the punches... Change is constant, and if you don't adapt, you're left behind. So when Andy McNally returns to find that Sam Swarek is now a Detective and that he's moved on, both professionally and personally, she's going to have to figure out how to adapt.