As David tells Ellie, he truly came to believe in god after the world ended and in how everything happens for a reason. But this wannabe John Locke is not here to eat oranges and play backgammon. David explains to Ellie how he sent four of his men out to scout and one didn’t come back because he got killed — by an older man and a little girl (at the end of the sixth episode). Realizing they know who she is, Ellie grabs the medicine before Troy Baker can kill her, and runs back to Joel.
The thing about David is that he is terrifyingly calm, and that makes him even scarier. It’s not when he gets angry that you realize he’s the worst — it’s when he acts suspiciously nice, telling his men not to hurt Ellie despite her being captured alive would mean one more mouth to feed. It’s how he promises his people that capturing (and executing) Joel is nothing but a call for justice, right before he hits a girl in the face for being angry that Joel and Ellie are responsible for her dad’s death. David is a man who promises you the world while holding a knife to your throat.
Back at the hideout, Ellie manages to inject Joel with the medicine, tells him that they are coming for him, and heads out to distract them while Joel recuperates — leaving him only with a knife. Sadly, murderous Troy Baker shoots down Ellie’s horse and captures her. As for Joel, he miraculously heals in just a few minutes, and right before one of David’s men finds his hiding spot, Joel stabs and kills him. Not only that, he becomes a killing machine, mowing down all of David’s men, and torturing a couple.