After centuries of being lied to and treated poorly by the Clave, the Downworlders decide to come together and take matters into their own hands as the hunt for Valentine and Sebastian intensifies. But what starts off as a way to preserve their own, the Downworlders choice to break with the Shadowhunters, could quickly escalate to war.
- Sebastian briefly held Jace captive, before Jace goaded Sebastian into freeing him so they could fight.
- Jace and Sebastian had a duel while Valentine was headed to Lake Lyn to summon Raziel.
- Sebastian gloated about how Valentine had taught him of a spot on a man's back that one could stab to pierce both the spine and the heart at the same time.
- Sebastian briefly bested Jace, but Isabelle arrived just before Sebastian could deliver a killing blow. She used her whip to grip his wrist and confronted him about hurting Max.
- While Sebastian was preoccupied with Isabelle, Jace was able to sneak up behind him to stab him in the aforementioned spot on his back that pierced his heart and would kill him.
- Sebastian's body fell into the river and floated away from Jace and Isabelle.