Simon is determined to get rid of the Mark of Cain and, with Isabelle's help, tries to track down New York's oldest vampire to get more information on the mark. Now in Paris, Clary desperately tries to find an escape from her current situation. Meanwhile, with his new sense of mortality, Magnus tries to live life to the very fullest.
In the emotional midseason premiere, everyone is dealing with the loss of Clary and are trying to move on best they can. Unbeknownst to them, the Shadowhunters face a new level of evil that they can't even imagine with the arrival of Jonathan Morgenstern.
In the climactic mid-season finale, the team scrambles to find a way to put a stop to Lilith’s plan coming to fruition. But going up against their biggest opponent yet, their odds are not looking good. Meanwhile, Simon makes a heartbreaking choice with Isabelle’s help and Magnus reconnects with a powerful person from his past.
Clary faces down an old foe in an attempt to find answers about Lilith’s plan. Alec and Magnus turn to Lorenzo Rey for help, while Lilith finds a new ally. Luke must choose between his pack and his family, as Simon is forced to deal with his past.
Magnus, Alec and Isabelle try to reach Jace inside The Owl, but even as powerful as Magnus is, can he help the Lightwoods retrieve their brother from his demon prison? Maia and Jordan join Simon on the hunt for Lilith, while Luke tries to find a way to get to Clary.
With the Owl’s identity revealed, Alec, Isabelle, and Clary head to Alicante to try and find a way to stop him. Luke and Simon team up to track Lilith’s latest possible victim. Maia reflects on her past.
Clary teams up with Magnus to investigate a recent demon attack. Simon is stunned with he’s visited by someone he never thought he’d see again, and who now won’t seem to leave. Meanwhile, Izzy worries about dinner with her family and a special guest and Luke reaches out to Maryse.
Someone is out to get Simon and Jace is on the hunt to find out who it is, meanwhile Clary turns to Luke to find a way to help Jace. Alec worries about the future of his relationship after learning more about Magnu's romantic past.
Jace’s concerns grow about his mental state and turns to Luke for information on his family’s past. Clary and Izzy go after a rogue vampire and Simon hunts for a new apartment.
The Shadowhunters try to track down the new imposing threat, while Jace has a suspicion that Jonathan is back and behind the mundane attacks. Simon tries to figure out what The Seelie Queen did to him during his time in the glade. Alec decides to host a Lightwood family dinner at Magnus’ house after a surprising visit from Maryse.
The Warlocks’ magic is becoming corrupted by a demonic presence while Izzy and Luke try to track down more information on the recent series of possessions.
Secrets abound as the shadowhunters and downworlders try to get back to normal after Valentine's death. Clary struggles with keeping her secret about Raziel's wish, while Alec pushes Jace to come clean about whatever Jace and Clary are hiding. Luke must use tough love to keep his secret hidden from Ollie who is on a war path for answers. And Magnus hides his true feelings about his new position in the Warlock community from Alec. Meanwhile, Lilith sets a plan in motion in New York City as Simon spend stime in the Seelie Court. MORE -LESS