The Last of Us Season 2 finale: What were Abby and her crew planning?

The Last of Us Season 2 ended on a slightly confusing, cliffhanger-y note, with plenty of death and lots of different moving parts.

But in amongst that final gunshot and Ellie (Bella Ramsey) becoming increasingly Joel-like (Pedro Pascal), there are also some subplots that remain mysterious.

One of these concerns Abby (Kaitlyn Dever) and her group, and the reason they're AWOL from the rest of the Washington Liberation Front (WLF). So what exactly are they planning when Ellie arrives to throw a spanner in the works?