With Luke in dire need of help, Jace, Clary and Simon take him to Magnus' lair in hopes of saving his life. Once there, the story of how Valentine came to be evil, and Jocelyn and Luke's past is revealed to Clary in hopes of triggering her memory of what happened to The Mortal Cup.

Meanwhile, Isabelle and Alec are tasked to restore their family name in the eyes of The Clave.

Clary and Jace get a tip from Meliorn that they can find Valentine by locating a portal in another dimension, but only Clary can venture into this new world. What Clary finds in this alternative universe is that life there is as if the threat of demons no longer existed and Shadowhunters were no longer needed. While she realizes that this dimension is the life she always dreamed of, Clary must act fast or she will lose herself in the alternative world forever.

Meanwhile, Alec and Isabelle must face the consequences of the Downworlder attack.

The hunt is on for Jace Wayland, and Alec and Isabelle hope to reach him before the rest of the Shadowhunters do. With orders from the Clave of “shoot to kill,” the Lightwood siblings must act fast. Also on his own search, Simon turns to Magnus for help when he finds himself at odds with both Raphael and Aldertree. Meanwhile, Clary struggles to find where she belongs since she doesn’t seem to fit into the Shadowhunter world, yet can’t go back to her mundane life.

Tasked with arranging his brother Max’s Rune Ceremony, Alex decides this would be the perfect opportunity for his family to get to know Magnus. But with tensions flying among the different Shadowhunters, Max’s big event quickly becomes an evening where they all must face their biggest fears. Meanwhile, Simon makes a bold move as Isabelle finds an unlikely new ally.