Big Season 3 Watch Online. In Season 3, Cassie, Jenny and newly appointed sheriff Beau Arlen maintain order in Helena, Montana with their unparalleled investigative skills. But when a local backcountry trip led by charismatic outfitter Sunny Barnes goes awry, the trio faces their most formidable mystery yet – in which no camper can be trusted and where danger lurks around every jagged rock and gnarled tree.