Meliorn is taking Jace and Clary through Seelie woods to look for a door to another dimension. Apparently, the Seelie woods are full of doors.
Meliorn says that if they find the portal attached to the portal shard on her necklace, it will take them to Valentine. But, only Clary can go, because it's only Clary that Meliorn owes the debt to.
Clary convinces Meliorn to let Jace come in once she finds the portal, so he can help her fight Valentine.
Back at the Institute, Alec confronts Izzy about her role in the Meliorn ambush. She is not being very cooperative. Lydia is questioning one of the other guards who was there, and he pretty much implicates Izzy.
Simon shows up at the Lone Wolf. He is oblivious to the whole werewolves and vampires hating each other thing. He doesn't get it, either. Before he's attacked though, Luke steps in. Simon tells him that Raphael appointed him ambassador to the werewolves.
Clary enters the alternate world and ends up in the kitchen at the loft. Valentine is there, but he's just her dad. She freaks out, though, and grabs a butter knife to use against him. She reunites with her mom. She's confused, but she snaps out of it and leaves.
Clary finds Alec, Simon, Izzy and Jace at the outdoor Java Juice bar. She finds out Valentine is holding a Mad Hatter Party at the Institute later. Jace kisses her and she almost falls into the world, but snaps out of it again and takes off.
Lydia arrests Izzy for high treason.
Simon and Luke are walking when the Internal Affairs guy shows up to arrest Luke. Simon goes crazy and attacks, but Luke stops him. The IA guy still thinks Luke is the demonic killer.
Meliorn and Jace are waiting for Clary outside the doorway. Meliorn starts feeling the presence of demons. He tells Jace they are attracted to the peacefulness of the Seelie woods.
Clary finds Magnus and tries to convince him to use his magic to help her find the portal. At first he doesn't believe her, but then he does and puts together a potion to try to get his magic back. It doesn't work, but when he touches Clary's portal shard, it does. He discovers the portal she's looking for is at the Institute. She invites him to the party to help her find it later.
Alec tells Lydia all about the ambush and who was present. He tells her he has the mortal cup and will exchange it if they let Izzy go. He goes to find it, but it's gone. He knows Jace took it.
Alec visits Izzy and tells her he's going to use his parabati track to find Jace to get the mortal cup back. She doesn't want him to, but he finds Hodge and they perform some rune ritual.
Simon is holding the IA guy hostage. He claims he is the demonic killer and is going to pump all the blood out of the guy. The guy freaks out, but Luke comes to the rescue, shooting and "killing" Simon.
It's party time at the Institute. Jace meets up with Clary. Valentine introduces himself to Jace. Magnus shows up, but he isn't on the guest list. Alec sees him and lets him in. Magnus is intrigued, but he's there for a reason.
A demon shows up and Meliorn and Jace fight it, but the rune ritual Hodge is performing on Alec causes Jace to weaken. The demon beats both Jace and Meliorn and jumps into the doorway. Alec sees where Jace is.
At the party, Magnus finds Clary, but she doesn't know who he is at first. Eventually, she snaps out of it and they go to the Institute's basement to find the portal. Jace sees them and gets jealous. He follows them down there, accuses Clary of cheating, and breaks up with her.
At the morgue, Luke verifies that the "dead" Simon is the demonic killer. The IA guy thanks Luke for saving his life. After he leaves, Simon zips himself out of the bag. He seems to be loving the vamp life. Alarec tells Simon the werewolves are indebted to him.
Jace convinces Meliorn to let him into the doorway to fight the demon. He does. The doorway disappears just as Alec and Lydia get there. Jace shows up in the basement where Clary is. He fights the demon, but gets bit. Magnus finds the portal and Clary and Jace enter.
Alec tells Izzy they couldn't get to Jace and tells her Lydia helped him. She's sort of impressed.
Jace and Clary end up in Valentine's lab at Chernobyl. No one is there, but someone is banging on a locker. Jace opens the locker and it's Michael Wayland, his dad, that he thought was dead.