Damien, who is Batman's son and the new Robin, is having some attitude problems. In fact, he messes up one of the Leagues missions. So Batman has Nightwing (the original Robin) to the headquarters of the Teen Titans, where he can be with superheroes his own age and learn to work as part of a team. He picks a fight with Blue Beetle and is horribly scorched-but Raven's power heals him so he's okay. He can relate more to her because of his mother's lineage.
The Justice League is taken over by the demon Trigon, who just happens to be the father of the Teen Titan's Raven. The two groups end up fighting until the League is no longer controlled-then they deal with the demon together.
This is animated film is a good followup to SON OF BATMAN and BATMAN: BAD BLOOD. Recommended.