It is 19 years before the battle of Yavin, the Republic is nearing its downfall in the dying days of the Clone Wars.
Two Jedi knights are both on a mission together when Order 66 is issued. They have no clones with them and do not even know what has happened. Then they discover that the Jedi have been branded traitors to the Republic, and that their kind are being extinguished across the galaxy.
It's all about survival.