Immediately after the events of The Desolation of Smaug, Bilbo and the dwarves try to defend Erebor's mountain of treasure from others who claim it: the men of the ruined Laketown and the elves of Mirkwood. Meanwhile an army of Orcs led by Azog the Defiler is marching on Erebor, fueled by the rise of the dark lord Sauron. Dwarves, elves and men must unite, and the hope for Middle-Earth falls into Bilbo's hands.
Watched with my youngest (8). She found this much more confusing than the previous films, with random armies appearing out of nowhere.
For my money… I get that you want your character deaths to have a bit of meaning, rather than being essentially a footnote as they are in the books, but wow this is laboured.