Based on the bestselling young adult fantasy book series The Mortal Instruments by Cassandra Clare, Shadowhunters follows 18-year-old Clary Fray, who finds out on her birthday that she is not who she thinks she is but rather comes from a long line of Shadowhunters - human-angel hybrids who hunt down demons. When her mother, Jocelyn, is kidnapped, Clary is thrown into the world of demon hunting with mysterious Shadowhunter Jace and her best friend, Simon. Now living among faeries, warlocks, vampires and werewolves, Clary begins a journey of self-discovery as she learns more about her past and what her future may hold.
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 the warpath for answers. 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 spends time in the Seelie Court.
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.
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.
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.