I suspected that Princess Diana of Themyscira would have to face off against a god and I was right. Much like the comic books she and the other Amazonian people are constantly doing battle with Ares, god of war.
Chris Pine gave a little more info about his character
I play a pilot Who works for the Allies and spies on the Germans without Their knowledge. My character steals a notebook filled with scientific formulas in an Ottoman base, he steals a plane but is shot down in the open sea.
The site goes on to say (with the help translate):
There is a deadly gas that could annihilate humanity. Ares is jealous of humanity, which is a creation of his father, the deceased Zeus. Ares reduced the Amazons to slavery. When they rebelled with Zeus rebelled Ares killed Zeus.
Diana Prince becomes Wonder Woman to help Steve Trevor (Chris Pine) and his squad in search of the one who wants to wipe humanity off the map with the deadly gas.