The main plot of Birds of Prey is said to have something to do with Harley Quinn and a gang of femme fatales going on a mission to save Cassandra Cain. The film is currently ongoing production, and set photos confirm that Harley will actually have a relationship with Cain prior to her abduction.
Check out these photos:
With Harley usually siding with the villains, it would make sense that she would have some friendly connection with Cain—urging her to do the heroic thing and try to rescue her. We don't really know why this Cassandra Cain will end up so important to the Black Mask (Ewan McGregor), but I have a feeling that she's connected to some kind of criminal organization. Maybe she's the daughter of a rival gang? I doubt she has some mystical powers like Iron Fist.
What's also fun is that we can see Harley carrying a huge bag of dog food around. In the comics, Harley actually takes care of a pack of laughing hyenas. We don't know if they'll appear in the film, but the dog food sure is a fun nod.
With Birds of Prey set to come out in February of next year, I guess we should expect the first teaser to drop six months prior. Maybe we could get it around August. I wouldn't put it past DC to tease us as early as July—during Comic-Con.
Catch Birds of Prey (and the Fantabulous Emancipation of One Harley Quinn) in theaters Feb. 7, 2020.