Simon screens Clary's call. A vampire at the bar convinces Simon to drink plasma; he gets hooked and the vampire leads him to a vampire bleeder den.
Magnus relives a flashback of finding his mother dead. He is going to support Alec in his decision about what he tells the Clave about Valentine. Alec is going to hide the assassination attempt. He plans to remove the circle rune so that Valentine can be transferred to Idris.
Clary desperately tries to contact Simon. She visits him and reassures him that she loves him. However, he doesn't believe she loves him the same way.
Valentine reveals that he injected Jace's mother with pure angel blood when she was pregnant. He raised Jace for that future purpose. The Institute removes the circle rune from his neck.
Luke checks in on Simon and asks him about a girl who was found dead; she was drained of her blood. The victim is the girl who Simon fed on at the blood den. Simon's prints were on the dead girl's bracelet.
Sebastian's cousin Eileen arrives at the Institute to check on him. They agree to have dinner, but he rushes home to the man locked in the room. The mysterious man looks like Sebastian; "Sebastian" has been assuming his identity with magic.
Luke and Clary worry about Simon; he believes Simon killed the Mundane. Simon goes to Raphael for help, but he will only help if Simon tells him how he became a Daylighter.
Fake Sebastian fools Eileen into believing he's the real thing. Meanwhile, the real Sebastian breaks out from his restraints and escapes the apartment.
Simon is arrested for the murder of Heidi (the dead Mundane), but he escapes the car after realizing he didn't kill her. Someone drained her from her feet. Quinn was the murderer and he confronts him in the blood den.
The two fight each other and Simon stabs Quinn through the heart with a stake.
Magnus shares another flashback from when he killed his step-father after finding his mother dead.
Fake Sebastian kills the real Sebastian as he tries to reach Izzy and Eileen.
Raphael glamors Luke's partner so that she forgets details of the Shadow world and Simon.
Simon asks for time away from Clary to think about their situation.
The Institute plans to send Valentine to Idris, but another Shadowhunter Duncan brings him to Sebastian instead. Sebastian kills Duncan for finishing the job. It's revealed that Sebastian is actually Jonathan Morgenstern in disguise and his body is entirely burnt.