Jack listened to Julia's explanation of everything that was going on. It made a lot more sense now. They were chosen because they were hand selected through intense research. They were the best for the job even if two of them seemed a little off. They walked into the forest and it seemed that something was wrong, enough for Julia to completely change direction to check on the Tree of Life and it's guardian. Once there he stayed far back as Julia said but it turns out that things were going to go wrong anyway. 

He quickly cloaked himself in shadow then used lightning from both hands to kill the Maidens as fast as possible, making sure to avoid the dragon. He didn't have to do too much, everyone else seemed to have the maidens under control. All they had to do was keep themselves alive for now while making sure no damage came to the tree or it's guardian.