Jordan and the Praetor try to track down Heidi, while the Shadowhunters try to locate Jonathan. Meanwhile, Luke looks to Maryse for help and Isabelle gets a possible lead on information on what is really going on in the Clave prisons.
In the Season 3 midseason finale, the team scrambles to find a way to put a stop to Lilith's plan coming to fruition. 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.
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 Magnus' romantic past.