Erchomai is the tenth episode and the second half of the two-hour midseason finale of Season 3 of Shadowhunters: The Mortal Instruments.


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.





  • Jacob Skiba as Young Jonathan
  • Neeraja Ramjee as Disciple 1
  • Daniel Coz as Disciple 2
  • Danielle Ayow as Admit Nurse
  • Samora Smallwood as Uniformed Officer
  • Luke Marty as Security Guard


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TMI 3x09-10 Promo Preview

Promo for the 2-hour Spring Finale


See more promotional images here and stills here



  • The title "Erchomai" is the romanized Greek word έρχομαι, which means "to go", "to come", or "I am coming". It is a reference to the books where, in City of Lost Souls, Sebastian left the message "Erchomai" at the New York Institute, ominously warning them of his return and retaliation.
  • Filming for this episode (and thus 3A) ended on December 6, 2017.[1][2]
  • This episode was originally set to air on May 29, 2018,[3] before the schedule was changed; it was announced in April that the episode will instead air alongside the 9th episode on May 15, 2018.[4]

The following are elements adapted from The Mortal Instruments book series:

For differences, see here.


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